Rollup merge of rust-lang#91870 - rusticstuff:macosx_min_version_reve…

…rt, r=Mark-Simulacrum

Revert setting a default for the MACOSX_DEPLOYMENT_TARGET env var for linking

This reverts commit b376f56, which is the main part of rust-lang#90499, because it turns out that this causes a good amount of breakage in crates relying on the old behavior. In particular `winit`, `coreaudio` and crates that depend on them are affected. Fixes rust-lang#91372.

Background:
Before rust-lang#90499 the behavior was the following: If MACOSX_DEPLOYMENT_TARGET is not set,  we pass the minimum supported OS version to LLVM but not to the linker. The linker default depends on the Xcode version and the version of the OS it is running on. That caused one known problem in libcurl with the most recent Xcode versions. rust-lang#90499 passed the minumum supported version (10.7 for Macos x86-64) to the linker instead. This has shown to be problematic because some crates such as winit, coreaudio implicitly expect a newer minimum OS version. The libcurl issue has been fixed independently (see alexcrichton/curl-rust#417), so a revert should not really be problematic.

Eventually we should probably mimic clang's behavior and fall back to the default of the currently configured Macos SDK for both the LLVM min os target version and MACOSX_DEPLOYMENT_TARGET for linking. That would entail looking at the `Version` property of the `SDKSettings.json` in the currently configured SDK.

compiler/rustc_target/src/spec/aarch64_apple_darwin.rs

@@ -9,7 +9,6 @@ pub fn target() -> Target {
     base.supported_sanitizers = SanitizerSet::ADDRESS | SanitizerSet::CFI | SanitizerSet::THREAD;
 
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-arch".to_string(), "arm64".to_string()]);
-    base.link_env.extend(super::apple_base::macos_link_env("arm64"));
     base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
 
     // Clang automatically chooses a more specific target based on

compiler/rustc_target/src/spec/apple_base.rs

@@ -79,18 +79,6 @@ pub fn macos_llvm_target(arch: &str) -> String {
     format!("{}-apple-macosx{}.{}.0", arch, major, minor)
 }
 
-pub fn macos_link_env(arch: &str) -> Vec<(String, String)> {
-    // Use the default deployment target for linking just as with the LLVM target if not
-    // specified via MACOSX_DEPLOYMENT_TARGET, otherwise the system linker would use its
-    // default which varies with Xcode version.
-    if env::var("MACOSX_DEPLOYMENT_TARGET").is_err() {
-        let default = macos_default_deployment_target(arch);
-        vec![("MACOSX_DEPLOYMENT_TARGET".to_string(), format!("{}.{}", default.0, default.1))]
-    } else {
-        vec![]
-    }
-}
-
 pub fn macos_link_env_remove() -> Vec<String> {
     let mut env_remove = Vec::with_capacity(2);
     // Remove the `SDKROOT` environment variable if it's clearly set for the wrong platform, which

compiler/rustc_target/src/spec/i686_apple_darwin.rs

@@ -5,7 +5,6 @@ pub fn target() -> Target {
     base.cpu = "yonah".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
-    base.link_env.extend(super::apple_base::macos_link_env("i686"));
     base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     // don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
     base.stack_probes = StackProbeType::Call;

compiler/rustc_target/src/spec/x86_64_apple_darwin.rs

@@ -10,7 +10,6 @@ pub fn target() -> Target {
         LinkerFlavor::Gcc,
         vec!["-m64".to_string(), "-arch".to_string(), "x86_64".to_string()],
     );
-    base.link_env.extend(super::apple_base::macos_link_env("x86_64"));
     base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     // don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
     base.stack_probes = StackProbeType::Call;