[ASan] Speculative fix for TestCases/Posix/interception-in-shared-lib-test.cc...

[ASan] Speculative fix for TestCases/Posix/interception-in-shared-lib-test.cc and TestCases/suppressions-library.cc on FreeBSD.

r233802 has moved the tests above to Posix/ and introduced %ld_flags_rpath_so and %ld_flags_rpath_exe,
which haven't been defined for FreeBSD.
We expect the flags to be the same on Linux and FreeBSD. If there's another reason for the tests to fail on FreeBSD,
they'll need to be disabled.

llvm-svn: 233822