[compiler-rt] moved __asan_schedule_unregister_globals out of anonymous namespace

Summary: Newer versions of clang complain that __asan_schedule_unregister_globals is unused. Moving it outside the anonymous namespace gets rid of that warning.

Reviewers: rnk, timurrrr

Subscribers: kubabrecka, dberris

Differential Revision: https://reviews.llvm.org/D25921

llvm-svn: 285010