This is the SystemZ part originally part of https://reviews.llvm.org/D102894.
On SystemZ, the vector ABI changes depending on the presence of hardware vector support. Therefore, each binary compiled with a visible vector ABI (e.g. calling an external function with a vector argument) should be marked with a .gnu_attribute describing this.
This adds support on SystemZ to emit a gnu attribute for the vector abi both to asm and object files.
clang-tidy: warning: invalid case style for function 'ParseGNUAttribute' [readability-identifier-naming]
not useful