only specify --target by default for -Zgcc-ld=lld on wasm

On macOS, it's not yet clear which cases of clang/OS/target/SDK version impact
how to find ld/lld/rust-lld. The --target is not needed on our current targets with
a vanilla config, but may be in some cases. Specifying it all the time breaks the 10.7+
targets on x64 macOS.

We try to only specify it on macOS if the linker flavors are different,
for possible cases of cross-compilation with `-Zgcc-ld=lld` but the
expectation is that it should be passed manually when needed in these
situations.

Author: lqd

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2822,11 +2822,30 @@ fn add_gcc_ld_path(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
                     // Implement the "linker flavor" part of -Zgcc-ld
                     // by asking cc to use some kind of lld.
                     cmd.arg("-fuse-ld=lld");
+
                     if !flavor.is_gnu() {
                         // Tell clang to use a non-default LLD flavor.
                         // Gcc doesn't understand the target option, but we currently assume
                         // that gcc is not used for Apple and Wasm targets (#97402).
-                        cmd.arg(format!("--target={}", sess.target.llvm_target));
+                        //
+                        // Note that we don't want to do that by default on macOS: e.g. passing a
+                        // 10.7 target to LLVM works, but not to recent versions of clang/macOS, as
+                        // shown in issue #101653 and the discussion in PR #101792.
+                        //
+                        // It could be required in some cases of cross-compiling with
+                        // `-Zgcc-ld=lld`, but this is generally unspecified, and we don't know
+                        // which specific versions of clang, macOS SDK, host and target OS
+                        // combinations impact us here.
+                        //
+                        // So we do a simple first-approximation until we know more of what the
+                        // Apple targets require (and which would be handled prior to hitting this
+                        // `-Zgcc-ld=lld` codepath anyway), but the expectation is that until then
+                        // this should be manually passed if needed. We specify the target when
+                        // targeting a different linker flavor on macOS, and that's also always
+                        // the case when targeting WASM.
+                        if sess.target.linker_flavor != sess.host.linker_flavor {
+                            cmd.arg(format!("--target={}", sess.target.llvm_target));
+                        }
                     }
                 }
             }