Details of sys-libs/glibc:

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space

make check failed for ${ABI}-${CTARGET}-$1
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE

make check failed for ${ABI}-${CTARGET}-$1
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE

make check failed for ${ABI}-${CTARGET}-$1
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE

make check failed for ${ABI}-${CTARGET}-$1
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE

make check failed for ${ABI}-${CTARGET}-$1
nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
PIE hardening not applied, as your compiler doesn't default to PIE

nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
glibc-2.4 is nptl-only!
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
Warning! Gentoo's GLIBC with NPTL enabled now behaves like the
glibc from almost every other distribution out there. This means
that glibc is compiled -twice-, once with linuxthreads and once
with nptl. The NPTL version is installed to lib/tls and is still
used by default. If you do not need nor want the linuxthreads
fallback, you can disable this behavior by adding nptlonly to
USE to save yourself some compile time.

nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
Warning! Gentoo's GLIBC with NPTL enabled now behaves like the
glibc from almost every other distribution out there. This means
that glibc is compiled -twice-, once with linuxthreads and once
with nptl. The NPTL version is installed to lib/tls and is still
used by default. If you do not need nor want the linuxthreads
fallback, you can disable this behavior by adding nptlonly to
USE to save yourself some compile time.

nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
Generating all locales; edit /etc/locale.gen to save time/space
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
You are using Xen but don't have -mno-tls-direct-seg-refs in your CFLAGS.
This will result in a 50% performance penalty, which is probably not what you want.
Warning! Gentoo's GLIBC with NPTL enabled now behaves like the
glibc from almost every other distribution out there. This means
that glibc is compiled -twice-, once with linuxthreads and once
with nptl. The NPTL version is installed to lib/tls and is still
used by default. If you do not need nor want the linuxthreads
fallback, you can disable this behavior by adding nptlonly to
USE to save yourself some compile time.

nptlonly or -nptl in USE, removing /${ROOT}$(alt_libdir)/tls...
removing /lib64 symlink and moving lib to lib64...
dont hit ctrl-c until this is done
Warning! Gentoo's GLIBC with NPTL enabled now behaves like the
glibc from almost every other distribution out there. This means
that glibc is compiled -twice-, once with linuxthreads and once
with nptl. The NPTL version is installed to lib/tls and is still
used by default. If you do not need nor want the linuxthreads
fallback, you can disable this behavior by adding nptlonly to
USE to save yourself some compile time.

downgrading glibc, still not recommended, but we'll do as you wish
You have \
architecture does not support it!