sanitizer_common: fix freebsd build error

Variable flags is not used. Remove it.

Suggested-by: randall77 (Keith Randall)
Review: https://reviews.llvm.org/D67928



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@372698 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed