[asan] Do not instrument accesses to profiling globals

It's only useful to asan-itize profiling globals while debugging llvm's
profiling instrumentation passes. Enabling asan along with instrprof or
gcov instrumentation shouldn't incur extra overhead.

This patch is in the same spirit as r264805 and r273202, which disabled
tsan instrumentation of instrprof/gcov globals.

Differential Revision: http://reviews.llvm.org/D21541

llvm-svn: 273444