Rollup merge of #137860 - taiki-e:powerpcspe-msync, r=workingjubilee

rustc_target: Add msync target feature and enable it on powerpcspe targets

Some older PowerPC processors do not have the `sync` (`sync 0`) and `lwsync` (`sync 1`) instructions, but instead have the `msync` instruction. (IIRC `msync` and `sync` will be assembled into the same bit-pattern, but `lwsync` will be SIGILL. See also https://gcc.gnu.org/legacy-ml/gcc-patches/2006-11/msg01238.html.)

LLVM recognizes this as the [`msync` feature](https://github.com/llvm/llvm-project/blob/cc5d8a4b2fc765c3c432f1ad0b185dae518d41bd/llvm/lib/Target/PowerPC/PPC.td#L140) and enables for some cpus such as [e500](https://github.com/llvm/llvm-project/blob/cc5d8a4b2fc765c3c432f1ad0b185dae518d41bd/llvm/lib/Target/PowerPC/PPC.td#L644).

powerpcspe is a target for CPUs such as e500 ([Debian Wiki](https://wiki.debian.org/PowerPCSPEPort)). However, the `msync` feature is currently not enabled except for vxworks, and at least since 2022-04, powerpc-unknown-linux-gnuspe was known to not work on real hardware without `-C target-cpu` (e.g., #96394, #117361).

https://github.com/rust-lang/rust/blob/8c392966a013fd8a09e6b78b3c8d6e442bc278e1/compiler/rustc_target/src/spec/targets/powerpc_wrs_vxworks_spe.rs#L28

Fixes #117361

cc `@BKPepe` ([powerpc-unknown-linux-muslspe target maintainer](https://doc.rust-lang.org/nightly/rustc/platform-support/powerpc-unknown-linux-muslspe.html#target-maintainers))
cc `@glaubitz` (who added powerpc-unknown-linux-gnuspe in https://github.com/rust-lang/rust/pull/48484)
cc `@th0ma7` (who opened #117361)

r? workingjubilee

`@rustbot` label +O-PowerPC +A-target-feature

0 files changed, 0 insertions, 0 deletions