Allow to bootstrap compiler with the GCC backend

Author: GuillaumeGomez

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

@@ -20,7 +20,7 @@ use tracing::{instrument, span};
 
 use crate::core::build_steps::gcc::{Gcc, add_cg_gcc_cargo_flags};
 use crate::core::build_steps::tool::{RustcPrivateCompilers, SourceType, copy_lld_artifacts};
-use crate::core::build_steps::{dist, llvm};
+use crate::core::build_steps::{dist, gcc, llvm};
 use crate::core::builder;
 use crate::core::builder::{
     Builder, Cargo, Kind, RunConfig, ShouldRun, Step, StepMetadata, crate_description,
@@ -2348,6 +2348,19 @@ impl Step for Assemble {
         dist::maybe_install_llvm_runtime(builder, target_compiler.host, &sysroot);
         dist::maybe_install_llvm_target(builder, target_compiler.host, &sysroot);
 
+        if builder.config.gcc_enabled(target_compiler.host) {
+            let gcc::GccOutput { mut libgccjit } =
+                builder.ensure(gcc::Gcc { target: target_compiler.host });
+            let dst_libdir = sysroot.join("lib");
+            builder.install(&libgccjit, &dst_libdir, FileType::NativeLibrary);
+            if let Some(file_name) = libgccjit.file_name() {
+                let mut file_name = file_name.to_os_string();
+                file_name.push(".0");
+                libgccjit.set_file_name(file_name);
+                builder.install(&libgccjit, &dst_libdir, FileType::NativeLibrary);
+            }
+        }
+
         // Link the compiler binary itself into place
         let out_dir = builder.cargo_out(build_compiler, Mode::Rustc, host);
         let rustc = out_dir.join(exe("rustc-main", host));

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

@@ -583,6 +583,16 @@ impl Builder<'_> {
             rustflags.arg("--cfg=bootstrap");
         }
 
+        if self
+            .config
+            .default_codegen_backend(compiler.host)
+            .is_some_and(|backend| backend.is_gcc())
+        {
+            let sysroot = sysroot.join("lib");
+            let sysroot_str = sysroot.as_os_str().to_str().expect("sysroot should be UTF-8");
+            cargo.env("LD_LIBRARY_PATH", sysroot_str);
+        }
+
         if cmd_kind == Kind::Clippy {
             // clippy overwrites sysroot if we pass it to cargo.
             // Pass it directly to clippy instead.

src/bootstrap/src/core/config/config.rs

@@ -1774,6 +1774,10 @@ impl Config {
         self.enabled_codegen_backends(target).contains(&CodegenBackendKind::Llvm)
     }
 
+    pub fn gcc_enabled(&self, target: TargetSelection) -> bool {
+        self.enabled_codegen_backends(target).contains(&CodegenBackendKind::Gcc)
+    }
+
     pub fn llvm_libunwind(&self, target: TargetSelection) -> LlvmLibunwind {
         self.target_config
             .get(&target)