Add llvm.build-config option

config.toml.example

@@ -145,6 +145,9 @@ changelog-seen = 2
 # Whether to include the Polly optimizer.
 #polly = false
 
+# Custom CMake defines to set when building LLVM.
+#build-config = {}
+
 # =============================================================================
 # General build configuration options
 # =============================================================================

src/bootstrap/config.rs

@@ -104,6 +104,7 @@ pub struct Config {
     pub llvm_allow_old_toolchain: bool,
     pub llvm_polly: bool,
     pub llvm_from_ci: bool,
+    pub llvm_build_config: HashMap<String, String>,
 
     pub use_lld: bool,
     pub lld_enabled: bool,
@@ -432,6 +433,7 @@ struct Llvm {
     allow_old_toolchain: Option<bool>,
     polly: Option<bool>,
     download_ci_llvm: Option<StringOrBool>,
+    build_config: Option<HashMap<String, String>>,
 }
 
 #[derive(Deserialize, Default, Clone, Merge)]
@@ -743,6 +745,7 @@ impl Config {
             config.llvm_use_linker = llvm.use_linker.clone();
             config.llvm_allow_old_toolchain = llvm.allow_old_toolchain.unwrap_or(false);
             config.llvm_polly = llvm.polly.unwrap_or(false);
+            config.llvm_build_config = llvm.build_config.clone().unwrap_or(Default::default());
             config.llvm_from_ci = match llvm.download_ci_llvm {
                 Some(StringOrBool::String(s)) => {
                     assert!(s == "if-available", "unknown option `{}` for download-ci-llvm", s);
@@ -789,6 +792,7 @@ impl Config {
                 check_ci_llvm!(llvm.use_linker);
                 check_ci_llvm!(llvm.allow_old_toolchain);
                 check_ci_llvm!(llvm.polly);
+                check_ci_llvm!(llvm.build_config);
 
                 // CI-built LLVM can be either dynamic or static.
                 let ci_llvm = config.out.join(&*config.build.triple).join("ci-llvm");

src/bootstrap/native.rs

@@ -317,6 +317,10 @@ impl Step for Llvm {
 
         configure_cmake(builder, target, &mut cfg, true);
 
+        for (key, val) in &builder.config.llvm_build_config {
+            cfg.define(key, val);
+        }
+
         // FIXME: we don't actually need to build all LLVM tools and all LLVM
         //        libraries here, e.g., we just want a few components and a few
         //        tools. Figure out how to filter them down and only build the right