[ASan] Fix the test for __asan_gen_ globals and actually fix http://llvm.org/bugs/show_bug.cgi?id=17976
by setting the correct linkage (as stated in the bug).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198018 91177308-0d34-0410-b5e6-96231b3b80d8