This fixes running tests with a toolchain that defaults to a MinGW
target.
After the previous attempt with this patch, this is now changed to
use !defined(__MINGW32__) instead of defined(_MSC_VER) to distinguish
between MSVC and MinGW mode; Clang doesn't define _MSC_VER when invoked
with "clang -cc1" as some of those tests do.
Differential Revision: https://reviews.llvm.org/D149997
Move -lc++experimental before -lc++abi (that was forgotten in the
original patch), and mark a test as UNSUPPORTED on AIX. I contacted
the owners of the AIX bot that failed because I was unable to reproduce
the issue locally.
Based on the discussion at [1], this patch adds a Clang flag called
-fexperimental-library that controls whether experimental library
features are provided in libc++. In essence, it links against the
experimental static archive provided by libc++ and defines a feature
that can be picked up by libc++ to enable experimental features.
This ensures that users don't start depending on experimental
(and hence unstable) features unknowingly.
[1]: https://discourse.llvm.org/t/rfc-a-compiler-flag-to-enable-experimental-unstable-language-and-library-features
Differential Revision: https://reviews.llvm.org/D121141
