Install missing VSX headers (POWER) (#85547)
E.g. `test_cpp_extensions_aot_ninja` fails as it includes `vec.h` which requires the vec/vsx/* headers and `sleef.h`. The latter is also required for AVX512 builds on non MSVC compilers.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85547
Approved by: https://github.com/kit1980
