sys-libs/glibc: Revbump 2.26-r6 with next patchset (patchlevel 6)

sys-libs/glibc: Revbump 2.26-r6 with next patchset (patchlevel 6)

10 test failures need investigating:
===
FAIL: elf/tst-prelink-cmp
XPASS: elf/tst-protected1a
XPASS: elf/tst-protected1b
FAIL: malloc/tst-malloc-tcache-leak
FAIL: math/test-float128-finite-tgamma
FAIL: math/test-float128-finite-trunc
FAIL: math/test-float128-tgamma
FAIL: math/test-float128-trunc
FAIL: math/test-ifloat128-tgamma
FAIL: math/test-ifloat128-trunc
FAIL: misc/tst-ttyname
UNSUPPORTED: nptl/test-cond-printers
UNSUPPORTED: nptl/test-condattr-printers
UNSUPPORTED: nptl/test-mutex-printers
UNSUPPORTED: nptl/test-mutexattr-printers
UNSUPPORTED: nptl/test-rwlock-printers
UNSUPPORTED: nptl/test-rwlockattr-printers
FAIL: nss/tst-nss-files-hosts-multi
Summary of test results:
     10 FAIL
   4113 PASS
      6 UNSUPPORTED
     29 XFAIL
      2 XPASS
===

Bug: https://bugs.gentoo.org/646492
Bug: https://bugs.gentoo.org/646490
Bug: https://bugs.gentoo.org/641644
Bug: https://bugs.gentoo.org/644278
Package-Manager: Portage-2.3.21, Repoman-2.3.6