sys-libs/glibc: avoid RESTRICT=strip and use 'dostrip -x /'

sys-libs/glibc: avoid RESTRICT=strip and use 'dostrip -x /'

RESTRICT=strip + 'dostrip /' does not have a desired effect
of enabling (possibly selective) stripping in portage:
https://bugs.gentoo.org/697960

Workaround it by using 'if foo && dostrip -x /' instead of
RESTRICT=strip + 'if foo || dostrip /'.

Reported-by: Arfrever Frehtes Taifersar Arahesis
Fixed-by: Arfrever Frehtes Taifersar Arahesis
Package-Manager: Portage-2.3.76, Repoman-2.3.17
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>