Rollup merge of #138451 - Kobzol:gcc-ci-build-gcc, r=GuillaumeGomez

Build GCC on CI with GCC, not Clang

It seems that GCC built with Clang misbehaves. I have tested that cg_gcc tests [pass](https://github.com/rust-lang/rust/actions/runs/13842365913/job/38732750617?pr=138451) on CI with a downloaded GCC that was built in this way.

Prerequisite for https://github.com/rust-lang/rust/pull/138395.

r? ```@ghost```

3 files changed, 36 insertions, 15 deletions

diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index c393eb55c62..2354fe1ebaf 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -2481,7 +2481,7 @@ impl Step for Gcc {
     fn run(self, builder: &Builder<'_>) -> Self::Output {
         let tarball = Tarball::new(builder, "gcc", &self.target.triple);
         let output = builder.ensure(super::gcc::Gcc { target: self.target });
-        tarball.add_file(output.libgccjit, ".", 0o644);
+        tarball.add_file(output.libgccjit, "lib", 0o644);
         tarball.generate()
     }
 }
diff --git a/src/bootstrap/src/core/build_steps/gcc.rs b/src/bootstrap/src/core/build_steps/gcc.rs
index 5a4bc9bdbcb..0aa2a332531 100644
--- a/src/bootstrap/src/core/build_steps/gcc.rs
+++ b/src/bootstrap/src/core/build_steps/gcc.rs
@@ -63,11 +63,7 @@ impl Step for Gcc {
         }
 
         build_gcc(&metadata, builder, target);
-
-        let lib_alias = metadata.install_dir.join("lib/libgccjit.so.0");
-        if !lib_alias.exists() {
-            t!(builder.symlink_file(&libgccjit_path, lib_alias));
-        }
+        create_lib_alias(builder, &libgccjit_path);
 
         t!(metadata.stamp.write());
 
@@ -75,6 +71,15 @@ impl Step for Gcc {
     }
 }
 
+/// Creates a libgccjit.so.0 alias next to libgccjit.so if it does not
+/// already exist
+fn create_lib_alias(builder: &Builder<'_>, libgccjit: &PathBuf) {
+    let lib_alias = libgccjit.parent().unwrap().join("libgccjit.so.0");
+    if !lib_alias.exists() {
+        t!(builder.symlink_file(libgccjit, lib_alias));
+    }
+}
+
 pub struct Meta {
     stamp: BuildStamp,
     out_dir: PathBuf,
@@ -109,8 +114,10 @@ fn try_download_gcc(builder: &Builder<'_>, target: TargetSelection) -> Option<Pa
         builder.config.download_ci_gcc(&sha, &root);
         t!(gcc_stamp.write());
     }
-    // FIXME: put libgccjit.so into a lib directory in dist::Gcc
-    Some(root.join("libgccjit.so"))
+
+    let libgccjit = root.join("lib").join("libgccjit.so");
+    create_lib_alias(builder, &libgccjit);
+    Some(libgccjit)
 }
 
 #[cfg(test)]
@@ -177,6 +184,14 @@ fn libgccjit_built_path(install_dir: &Path) -> PathBuf {
 }
 
 fn build_gcc(metadata: &Meta, builder: &Builder<'_>, target: TargetSelection) {
+    if builder.build.cc_tool(target).is_like_clang()
+        || builder.build.cxx_tool(target).is_like_clang()
+    {
+        panic!(
+            "Attempting to build GCC using Clang, which is known to misbehave. Please use GCC as the host C/C++ compiler. "
+        );
+    }
+
     let Meta { stamp: _, out_dir, install_dir, root } = metadata;
 
     t!(fs::create_dir_all(out_dir));
@@ -203,18 +218,13 @@ fn build_gcc(metadata: &Meta, builder: &Builder<'_>, target: TargetSelection) {
     let mut configure_cmd = command(src_dir.join("configure"));
     configure_cmd
         .current_dir(out_dir)
-        // On CI, we compile GCC with Clang.
-        // The -Wno-everything flag is needed to make GCC compile with Clang 19.
-        // `-g -O2` are the default flags that are otherwise used by Make.
-        // FIXME(kobzol): change the flags once we have [gcc] configuration in config.toml.
-        .env("CXXFLAGS", "-Wno-everything -g -O2")
-        .env("CFLAGS", "-Wno-everything -g -O2")
         .arg("--enable-host-shared")
-        .arg("--enable-languages=jit")
+        .arg("--enable-languages=c,jit,lto")
         .arg("--enable-checking=release")
         .arg("--disable-bootstrap")
         .arg("--disable-multilib")
         .arg(format!("--prefix={}", install_dir.display()));
+
     let cc = builder.build.cc(target).display().to_string();
     let cc = builder
         .build
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 8dfd1bbfd60..91574f8bf5d 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -27,6 +27,7 @@ use std::{env, fs, io, str};
 
 use build_helper::ci::gha;
 use build_helper::exit;
+use cc::Tool;
 use termcolor::{ColorChoice, StandardStream, WriteColor};
 use utils::build_stamp::BuildStamp;
 use utils::channel::GitInfo;
@@ -1218,6 +1219,16 @@ Executed at: {executed_at}"#,
         self.cc.borrow()[&target].path().into()
     }
 
+    /// Returns the internal `cc::Tool` for the C compiler.
+    fn cc_tool(&self, target: TargetSelection) -> Tool {
+        self.cc.borrow()[&target].clone()
+    }
+
+    /// Returns the internal `cc::Tool` for the C++ compiler.
+    fn cxx_tool(&self, target: TargetSelection) -> Tool {
+        self.cxx.borrow()[&target].clone()
+    }
+
     /// Returns C flags that `cc-rs` thinks should be enabled for the
     /// specified target by default.
     fn cc_handled_clags(&self, target: TargetSelection, c: CLang) -> Vec<String> {