Always set the deployment target when building std

src/bootstrap/src/core/build_steps/compile.rs

@@ -1541,7 +1541,8 @@ pub fn compiler_file(
         return PathBuf::new();
     }
     let mut cmd = command(compiler);
-    cmd.args(builder.cflags(target, GitRepo::Rustc, c));
+    cmd.args(builder.default_cflags(target, c));
+    cmd.args(builder.extra_cflags(target, GitRepo::Rustc, c));
     cmd.arg(format!("-print-file-name={file}"));
     let out = cmd.run_capture_stdout(builder).stdout();
     PathBuf::from(out.trim())

src/bootstrap/src/core/build_steps/llvm.rs

@@ -757,9 +757,15 @@ fn configure_cmake(
     }
 
     cfg.build_arg("-j").build_arg(builder.jobs().to_string());
+    // FIXME(madsmtm): Allow `cmake-rs` to select flags by itself by passing
+    // our flags via `.cflag`/`.cxxflag` instead.
+    //
+    // Needs `suppressed_compiler_flag_prefixes` to be gone, and hence
+    // https://github.com/llvm/llvm-project/issues/88780 to be fixed.
     let mut cflags: OsString = builder
-        .cflags(target, GitRepo::Llvm, CLang::C)
+        .default_cflags(target, CLang::C)
         .into_iter()
+        .chain(builder.extra_cflags(target, GitRepo::Llvm, CLang::C))
         .filter(|flag| {
             !suppressed_compiler_flag_prefixes
                 .iter()
@@ -778,8 +784,9 @@ fn configure_cmake(
     }
     cfg.define("CMAKE_C_FLAGS", cflags);
     let mut cxxflags: OsString = builder
-        .cflags(target, GitRepo::Llvm, CLang::Cxx)
+        .default_cflags(target, CLang::Cxx)
         .into_iter()
+        .chain(builder.extra_cflags(target, GitRepo::Llvm, CLang::Cxx))
         .filter(|flag| {
             !suppressed_compiler_flag_prefixes
                 .iter()

src/bootstrap/src/core/build_steps/test.rs

@@ -2005,14 +2005,18 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         // Only pass correct values for these flags for the `run-make` suite as it
         // requires that a C++ compiler was configured which isn't always the case.
         if !builder.config.dry_run() && mode == "run-make" {
+            let mut cflags = builder.default_cflags(target, CLang::C);
+            cflags.extend(builder.extra_cflags(target, GitRepo::Rustc, CLang::C));
+            let mut cxxflags = builder.default_cflags(target, CLang::Cxx);
+            cxxflags.extend(builder.extra_cflags(target, GitRepo::Rustc, CLang::Cxx));
             cmd.arg("--cc")
                 .arg(builder.cc(target))
                 .arg("--cxx")
                 .arg(builder.cxx(target).unwrap())
                 .arg("--cflags")
-                .arg(builder.cflags(target, GitRepo::Rustc, CLang::C).join(" "))
+                .arg(cflags.join(" "))
                 .arg("--cxxflags")
-                .arg(builder.cflags(target, GitRepo::Rustc, CLang::Cxx).join(" "));
+                .arg(cxxflags.join(" "));
             copts_passed = true;
             if let Some(ar) = builder.ar(target) {
                 cmd.arg("--ar").arg(ar);

src/bootstrap/src/core/builder/cargo.rs

@@ -317,7 +317,7 @@ impl Cargo {
             let cc = ccacheify(&builder.cc(target));
             self.command.env(format!("CC_{triple_underscored}"), &cc);
 
-            let cflags = builder.cflags(target, GitRepo::Rustc, CLang::C).join(" ");
+            let cflags = builder.extra_cflags(target, GitRepo::Rustc, CLang::C).join(" ");
             self.command.env(format!("CFLAGS_{triple_underscored}"), &cflags);
 
             if let Some(ar) = builder.ar(target) {
@@ -329,7 +329,7 @@ impl Cargo {
 
             if let Ok(cxx) = builder.cxx(target) {
                 let cxx = ccacheify(&cxx);
-                let cxxflags = builder.cflags(target, GitRepo::Rustc, CLang::Cxx).join(" ");
+                let cxxflags = builder.extra_cflags(target, GitRepo::Rustc, CLang::Cxx).join(" ");
                 self.command
                     .env(format!("CXX_{triple_underscored}"), &cxx)
                     .env(format!("CXXFLAGS_{triple_underscored}"), cxxflags);

src/bootstrap/src/lib.rs

@@ -246,6 +246,7 @@ impl Mode {
     }
 }
 
+#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum CLang {
     C,
     Cxx,
@@ -1139,9 +1140,9 @@ Executed at: {executed_at}"#,
         self.cc.borrow()[&target].path().into()
     }
 
-    /// Returns a list of flags to pass to the C compiler for the target
-    /// specified.
-    fn cflags(&self, target: TargetSelection, which: GitRepo, c: CLang) -> Vec<String> {
+    /// Returns C flags that `cc-rs` thinks should be enabled for the
+    /// specified target by default.
+    fn default_cflags(&self, target: TargetSelection, c: CLang) -> Vec<String> {
         if self.config.dry_run() {
             return Vec::new();
         }
@@ -1150,14 +1151,18 @@ Executed at: {executed_at}"#,
             CLang::Cxx => self.cxx.borrow()[&target].clone(),
         };
 
-        // Filter out -O and /O (the optimization flags) that we picked up from
-        // cc-rs because the build scripts will determine that for themselves.
-        let mut base = base
-            .args()
+        // Filter out -O and /O (the optimization flags) that we picked up
+        // from cc-rs, that's up to the caller to figure out.
+        base.args()
             .iter()
             .map(|s| s.to_string_lossy().into_owned())
             .filter(|s| !s.starts_with("-O") && !s.starts_with("/O"))
-            .collect::<Vec<String>>();
+            .collect::<Vec<String>>()
+    }
+
+    /// Returns extra C flags that `cc-rs` doesn't handle.
+    fn extra_cflags(&self, target: TargetSelection, which: GitRepo, c: CLang) -> Vec<String> {
+        let mut base = Vec::new();
 
         // If we're compiling C++ on macOS then we add a flag indicating that
         // we want libc++ (more filled out than libstdc++), ensuring that

src/bootstrap/src/utils/cc_detect.rs

@@ -142,7 +142,8 @@ pub fn find_target(build: &Build, target: TargetSelection) {
     };
 
     build.cc.borrow_mut().insert(target, compiler.clone());
-    let cflags = build.cflags(target, GitRepo::Rustc, CLang::C);
+    let mut cflags = build.default_cflags(target, CLang::C);
+    cflags.extend(build.extra_cflags(target, GitRepo::Rustc, CLang::C));
 
     // If we use llvm-libunwind, we will need a C++ compiler as well for all targets
     // We'll need one anyways if the target triple is also a host triple
@@ -168,7 +169,8 @@ pub fn find_target(build: &Build, target: TargetSelection) {
     build.verbose(|| println!("CC_{} = {:?}", target.triple, build.cc(target)));
     build.verbose(|| println!("CFLAGS_{} = {cflags:?}", target.triple));
     if let Ok(cxx) = build.cxx(target) {
-        let cxxflags = build.cflags(target, GitRepo::Rustc, CLang::Cxx);
+        let mut cxxflags = build.default_cflags(target, CLang::Cxx);
+        cxxflags.extend(build.extra_cflags(target, GitRepo::Rustc, CLang::Cxx));
         build.verbose(|| println!("CXX_{} = {cxx:?}", target.triple));
         build.verbose(|| println!("CXXFLAGS_{} = {cxxflags:?}", target.triple));
     }