Auto merge of #88250 - rusticstuff:macos-lld, r=nagisa

Make `-Z gcc-ld=lld` work for Apple targets

`-Z gcc-ld=lld` was introduced in #85961. It does not work on Macos because lld needs be either named `ld64` or passed `-flavor darwin` as the first two arguments in order to select the Mach-O flavor. Rust invokes cc (=clang) on Macos for linking which calls `ld` as linker binary and not `ld64`, so just creating an `ld64` binary and modifying the search path with `-B` does not work.

In order to solve this patch does:
* Set the `lld_flavor` for all Apple-derived targets to `LldFlavor::Ld64`. As far as I can see this actually works towards fixing `-Xlinker=rust-lld` as all those targets use the Mach-O object format.
* Copy/hardlink rust-lld to the gcc-ld subdirectory as ld64 next to ld.
* If `-Z gcc-ld=lld` is used and the target lld flavor is Ld64 add `-fuse-ld=/path/to/ld64` to the linker invocation.

Fixes #86945.

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_target/src/spec/apple_base.rs b/compiler/rustc_target/src/spec/apple_base.rs
index 5d75f6ab39c..a21b784e11b 100644
--- a/compiler/rustc_target/src/spec/apple_base.rs
+++ b/compiler/rustc_target/src/spec/apple_base.rs
@@ -1,6 +1,6 @@
 use std::env;
 
-use crate::spec::{FramePointer, SplitDebuginfo, TargetOptions};
+use crate::spec::{FramePointer, LldFlavor, SplitDebuginfo, TargetOptions};
 
 pub fn opts(os: &str) -> TargetOptions {
     // ELF TLS is only available in macOS 10.7+. If you try to compile for 10.6
@@ -35,6 +35,7 @@ pub fn opts(os: &str) -> TargetOptions {
         abi_return_struct_as_int: true,
         emit_debug_gdb_scripts: false,
         eh_frame_header: false,
+        lld_flavor: LldFlavor::Ld64,
 
         // The historical default for macOS targets is to run `dsymutil` which
         // generates a packed version of debuginfo split from the main file.