Rollup merge of #144987 - tgross35:llvm21-f16-f128, r=nikic

Enable f16 and f128 on targets that were fixed in LLVM21

LLVM21 fixed the new float types on a number of targets:

* SystemZ gained f16 support  llvm/llvm-project#109164
* Hexagon now uses soft f16 to avoid recursion bugs  llvm/llvm-project#130977
* Mips now correctly handles f128 (actually since LLVM20) llvm/llvm-project#117525
* f128 is now correctly aligned when passing the stack on x86  llvm/llvm-project#138092

Thus, enable the types on relevant targets for LLVM > 21.0.0.

NVPTX also gained handling of f128 as a storage type, but it lacks support for basic math operations so is still disabled here.

try-job: dist-i586-gnu-i586-i686-musl
try-job: dist-i686-linux
try-job: dist-i686-msvc
try-job: dist-s390x-linux
try-job: dist-various-1
try-job: dist-various-2
try-job: dist-x86_64-linux
try-job: i686-gnu-1
try-job: i686-gnu-2
try-job: i686-msvc-1
try-job: i686-msvc-2
try-job: test-various

Author: tgross35