Some tests under fail unless _LIBCPP_ENABLE_EXPERIMENTAL is explicitly defined during compilation.

[mrashad32]

I noticed that some tests under libcxx/test/std/experimental/simd/ fail to build unless I manually define the macro _LIBCPP_ENABLE_EXPERIMENTAL.

For example, this test:
libcxx/test/std/experimental/simd/simd.class/simd_width.pass.cpp

I think this can be confusing for people running the tests, especially if they don’t know that this macro is needed.

So my question is, to add this to the additional flags will be a good suggestion?

Thanks