Add gcc bootstrap config section

Author: Kobzol

config.example.toml

@@ -163,6 +163,11 @@
 # Custom CMake defines to set when building LLVM.
 #build-config = {}
 
+# =============================================================================
+# Tweaking how GCC is compiled
+# =============================================================================
+[gcc]
+
 # =============================================================================
 # General build configuration options
 # =============================================================================

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

@@ -676,6 +676,7 @@ pub(crate) struct TomlConfig {
 build:Option<Build>,
 install:Option<Install>,
 llvm:Option<Llvm>,
+gcc:Option<Gcc>,
 rust:Option<Rust>,
 target:Option<HashMap<String,TomlTarget>>,
 dist:Option<Dist>,
@@ -710,7 +711,7 @@ trait Merge {
 implMergeforTomlConfig{
 fnmerge(
 &mutself,
-TomlConfig{ build, install, llvm, rust, dist, target, profile, change_id }:Self,
+TomlConfig{ build, install, llvm,gcc,rust, dist, target, profile, change_id }:Self,
 replace:ReplaceOpt,
 ){
 fndo_merge<T:Merge>(x:&mutOption<T>,y:Option<T>,replace:ReplaceOpt){
@@ -729,6 +730,7 @@ impl Merge for TomlConfig {
 do_merge(&mutself.build, build, replace);
 do_merge(&mutself.install, install, replace);
 do_merge(&mutself.llvm, llvm, replace);
+do_merge(&mutself.gcc, gcc, replace);
 do_merge(&mutself.rust, rust, replace);
 do_merge(&mutself.dist, dist, replace);
 
@@ -995,6 +997,11 @@ define_config! {
 }
 }
 
+define_config!{
+/// TOML representation of how the GCC build is configured.
+structGcc{}
+}
+
 define_config!{
 structDist{
  sign_folder:Option<String> = "sign-folder",