rustc_target: callconv: powerpc64: Use the ABI set in target options instead of guessing#150468

Gelbpunkt wants to merge 2 commits intorust-lang:mainrust-lang/rust:mainfrom

Gelbpunkt:rustc-target-callconv-spec-elf-abiGelbpunkt/rust:rustc-target-callconv-spec-elf-abiCopy head branch name to clipboard