Bootstrap: Don't duplicate cc-rs flags

Commands that end up invoking cc-rs, i.e. Cargo (through build scripts)
and cmake-rs don't need the CFLAGS from cc-rs itself, as they will just
end up as duplicates.

Author: madsmtm

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

@@ -758,7 +758,7 @@ fn configure_cmake(
 
     cfg.build_arg("-j").build_arg(builder.jobs().to_string());
     let mut cflags: OsString = builder
-        .cflags(target, GitRepo::Llvm, CLang::C)
+        .extra_cflags(target, GitRepo::Llvm, CLang::C)
         .into_iter()
         .filter(|flag| {
             !suppressed_compiler_flag_prefixes
@@ -778,7 +778,7 @@ fn configure_cmake(
     }
     cfg.define("CMAKE_C_FLAGS", cflags);
     let mut cxxflags: OsString = builder
-        .cflags(target, GitRepo::Llvm, CLang::Cxx)
+        .extra_cflags(target, GitRepo::Llvm, CLang::Cxx)
         .into_iter()
         .filter(|flag| {
             !suppressed_compiler_flag_prefixes

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

@@ -307,7 +307,7 @@ 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) {
@@ -319,7 +319,7 @@ 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

@@ -1207,6 +1207,18 @@ Executed at: {executed_at}"#,
             .filter(|s| !s.starts_with("-O") && !s.starts_with("/O"))
             .collect::<Vec<String>>();
 
+        base.extend(self.extra_cflags(target, which, c));
+
+        base
+    }
+
+    /// Returns a list of flags to pass to the C compiler for the target
+    /// specified, tailored for invocations that will end up invoking `cc-rs`
+    /// or `cmake-rs` (if we were to use `.cflags()` for those, we'd end up
+    /// duplicating the flags).
+    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
         // LLVM/etc are all properly compiled.