sys-libs/glibc: avoid GPREL overflow on ia64, bug #723268

sys-libs/glibc: avoid GPREL overflow on ia64, bug #723268

-fno-common had unintended side-effect to optimise more
accesses to global variables as module-local via GPREL22
relocations. Unfortunately glibc is large enough to overflow
GPREL22 offset.

Let's add a -fcommon workaround back to pessimize code slightly
that refers module-local globals. We'll need an equivalen of
-fPIC to do it consistently.

Bug: https://bugs.gentoo.org/723268
Package-Manager: Portage-2.3.99, Repoman-2.3.22
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>