buildtools: make AVX512 check portable

buildtools: make AVX512 check portable

buildtools/binutils-avx512-check.sh was Unix-only
and could not be used in cross builds:
1) written in shell;
2) used the assembler binary that may be missing,
   e.g. when building on Windows with LLVM;
3) located the assembler as ${AS:-as} and referenced objdump,
   but those binaries may be overridden via --cross-file.

Rewrite the script in Python.
Use the C compiler for the check.
Locate objdump and the C compiler using Meson.

Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>