bootstrap: Expose LLVM_USE_LINKER cmake option to config.toml.

config.toml.example

@@ -96,6 +96,10 @@
 # that your host compiler ships with libc++.
 #use-libcxx = true
 
+# The value specified here will be passed as `-DLLVM_USE_LINKER` to CMake.
+#use-linker = "lld"
+
+
 # =============================================================================
 # General build configuration options
 # =============================================================================

src/bootstrap/config.rs

@@ -77,6 +77,7 @@ pub struct Config {
     pub llvm_experimental_targets: String,
     pub llvm_link_jobs: Option<u32>,
     pub llvm_version_suffix: Option<String>,
+    pub llvm_use_linker: Option<String>,
 
     pub lld_enabled: bool,
     pub lldb_enabled: bool,
@@ -255,6 +256,7 @@ struct Llvm {
     version_suffix: Option<String>,
     clang_cl: Option<String>,
     use_libcxx: Option<bool>,
+    use_linker: Option<String>,
 }
 
 #[derive(Deserialize, Default, Clone)]
@@ -517,6 +519,7 @@ impl Config {
             config.llvm_version_suffix = llvm.version_suffix.clone();
             config.llvm_clang_cl = llvm.clang_cl.clone();
             set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
+            config.llvm_use_linker = llvm.use_linker.clone();
         }
 
         if let Some(ref rust) = toml.rust {

src/bootstrap/native.rs

@@ -231,6 +231,10 @@ impl Step for Llvm {
             cfg.define("LLVM_VERSION_SUFFIX", suffix);
         }
 
+        if let Some(ref linker) = builder.config.llvm_use_linker {
+            cfg.define("LLVM_USE_LINKER", linker);
+        }
+
         if let Some(ref python) = builder.config.python {
             cfg.define("PYTHON_EXECUTABLE", python);
         }