test: allow -target usage on Windows

When running the tests on Windows with a debug build, _DEBUG must be
added to the flags prior to the -target as the forced inclusion of a
header will prevent the compile test for the flag to fail.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@294716 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed