Found while running libc++'s test suite with MSVC's STL.
* In `escaped_output.unicode.pass.cpp`, replace `_LIBCPP_SHORT_WCHAR`
with `TEST_SHORT_WCHAR`.
+ This was the only test that was directly using the `_LIBCPP` macro.
`libcxx/test/support/test_macros.h` performs this mapping:
c60ac50939/libcxx/test/support/test_macros.h (L442-L444)
* In `msvc_stdlib_force_include.h`, define `TEST_SHORT_WCHAR`.