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

All PowerPC64 targets except AIX explicitly set the ABI in the target
options. We can therefore stop hardcoding the ABI to be used based on
the target environment or OS, except for the AIX special case.

The fallback based on endianness is kept for the sake of compatibility
with custom targets.

This makes it so that big endian targets not explicitly accounted for
before (powerpc64-unknown-openbsd) and targets that don't use the
expected default ABI (ELFv2 Glibc targets) use the correct ABI in the
calling convention code.

Signed-off-by: Jens Reidel <adrian@travitia.xyz>

Author: Gelbpunkt

compiler/rustc_target/src/callconv/powerpc64.rs

@@ -5,7 +5,7 @@
 use rustc_abi::{Endian, HasDataLayout, TyAbiInterface};
 
 use crate::callconv::{Align, ArgAbi, FnAbi, Reg, RegKind, Uniform};
-use crate::spec::{Env, HasTargetSpec, Os};
+use crate::spec::{Abi, HasTargetSpec, Os};
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 enum ABI {
@@ -106,8 +106,10 @@ where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
-    let abi = if cx.target_spec().env == Env::Musl || cx.target_spec().os == Os::FreeBsd {
+    let abi = if cx.target_spec().options.abi == Abi::ElfV2 {
         ELFv2
+    } else if cx.target_spec().options.abi == Abi::ElfV1 {
+        ELFv1
     } else if cx.target_spec().os == Os::Aix {
         AIX
     } else {