Rollup merge of rust-lang#132150 - taiki-e:ppc64-freebsd-abi, r=pnkfelix

Fix powerpc64 big-endian FreeBSD ABI

Note that FreeBSD version bump may be reverted due to rust-lang#120869 (comment). We may want to wait to merge this until that discussion is complete.

Fixes rust-lang#120869 (comment)

> > PPC64 FreeBSD (ELFv1 and ELFv2, version 13.2)
>
> It seems odd that ELFv1 and 13.N coexist.
>
> https://www.freebsd.org/releases/13.0R/relnotes/
>
> > powerpc64 switched to ELFv2 ABI at the same time it switched to LLVM. This brings us to a parity with modern Linux distributions. This also makes the binaries from previous FreeBSD versions incompatible with 13.0-RELEASE. Kernel still supports ELFv1, so jails and chroots using older FreeBSD versions are still compatible. [e4399d169acc](https://cgit.freebsd.org/src/commit/?id=e4399d169acc)
>
> Well, it is also odd that this target claims ELFv2 support since our ABI code does not use ELFv2 on this target.
>
> https://github.com/rust-lang/rust/blob/be01dabfefd2daa4574b974f571c7852085d60cb/compiler/rustc_target/src/callconv/powerpc64.rs#L102-L111

```@rustbot``` label +O-PowerPC +O-freebsd

compiler/rustc_target/src/callconv/powerpc64.rs

@@ -99,7 +99,7 @@ where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
-    let abi = if cx.target_spec().env == "musl" {
+    let abi = if cx.target_spec().env == "musl" || cx.target_spec().os == "freebsd" {
         ELFv2
     } else if cx.target_spec().os == "aix" {
         AIX

compiler/rustc_target/src/spec/targets/powerpc64_unknown_freebsd.rs

@@ -11,7 +11,7 @@ pub(crate) fn target() -> Target {
     Target {
         llvm_target: "powerpc64-unknown-freebsd".into(),
         metadata: crate::spec::TargetMetadata {
-            description: Some("PPC64 FreeBSD (ELFv1 and ELFv2)".into()),
+            description: Some("PPC64 FreeBSD (ELFv2)".into()),
             tier: Some(3),
             host_tools: Some(true),
             std: Some(true),

src/doc/rustc/src/platform-support.md

@@ -343,7 +343,7 @@ target | std | host | notes
 [`powerpc-unknown-openbsd`](platform-support/powerpc-unknown-openbsd.md) | * |  |
 [`powerpc-wrs-vxworks-spe`](platform-support/vxworks.md) | ✓ |  |
 [`powerpc-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
-`powerpc64-unknown-freebsd` | ✓ | ✓ | PPC64 FreeBSD (ELFv1 and ELFv2)
+`powerpc64-unknown-freebsd` | ✓ | ✓ | PPC64 FreeBSD (ELFv2)
 `powerpc64le-unknown-freebsd` | ✓ | ✓ | PPC64LE FreeBSD
 `powerpc-unknown-freebsd` | ? |   | PowerPC FreeBSD
 `powerpc64-unknown-linux-musl` | ? |  | 64-bit PowerPC Linux with musl 1.2.3