[clang] [compiler-rt] [llvm] [SystemZ] Add support for half (fp16) (PR #109164)

[Jonas Paulsson via cfe-commits]

JonPsson1 wrote:

Updated per review.

- strict fp-round / fp-extend added with tests.
- math functions like fsin promoted instead of expanded to non-existing fsinh.
- conversion functions from e.g. f16 -> f64 used instead of separate steps.
- __fp16 argument/return values removed (and tests in systemz-abi.c removed).
- docs/LanguageExtensions: SystemZ added as supporting _Float16.

Note on compiler-rt: not sure how to build llvm conversion functions and link them (have not tried this yet), but added the mapping in RuntimeLibcalls.cpp.


https://github.com/llvm/llvm-project/pull/109164