Don't link libm with -Wl,--as-needed on FreeBSD

Patch by jbeich (Jan Beich)

Differential Revision: https://reviews.llvm.org/D68051

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@374037 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed