test: allow -target usage on Windows
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: 756ef344af921d95d562d9e9f9389127a89a6314@294716 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx