Support passing cflags/cxxflags/ldflags to LLVM build

This may be needed with some host compilers.

config.toml.example

@@ -90,6 +90,11 @@
 # with clang-cl, so this is special in that it only compiles LLVM with clang-cl
 #clang-cl = '/path/to/clang-cl.exe'
 
+# Pass extra compiler and linker flags to the LLVM CMake build.
+#cflags = "-fextra-flag"
+#cxxflags = "-fextra-flag"
+#ldflags = "-Wl,extra-flag"
+
 # Use libc++ when building LLVM instead of libstdc++. This is the default on
 # platforms already use libc++ as the default C++ library, but this option
 # allows you to use libc++ even on platforms when it's not. You need to ensure

src/bootstrap/config.rs

@@ -82,6 +82,9 @@ pub struct Config {
     pub lldb_enabled: bool,
     pub llvm_tools_enabled: bool,
 
+    pub llvm_cflags: Option<String>,
+    pub llvm_cxxflags: Option<String>,
+    pub llvm_ldflags: Option<String>,
     pub llvm_use_libcxx: bool,
 
     // rust codegen options
@@ -254,6 +257,9 @@ struct Llvm {
     link_shared: Option<bool>,
     version_suffix: Option<String>,
     clang_cl: Option<String>,
+    cflags: Option<String>,
+    cxxflags: Option<String>,
+    ldflags: Option<String>,
     use_libcxx: Option<bool>,
 }
 
@@ -516,6 +522,10 @@ impl Config {
             config.llvm_link_jobs = llvm.link_jobs;
             config.llvm_version_suffix = llvm.version_suffix.clone();
             config.llvm_clang_cl = llvm.clang_cl.clone();
+
+            config.llvm_cflags = llvm.cflags.clone();
+            config.llvm_cxxflags = llvm.cxxflags.clone();
+            config.llvm_ldflags = llvm.ldflags.clone();
             set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
         }
 

src/bootstrap/configure.py

@@ -64,6 +64,10 @@ o("lldb", "rust.lldb", "build lldb")
 o("missing-tools", "dist.missing-tools", "allow failures when building tools")
 o("use-libcxx", "llvm.use_libcxx", "build LLVM with libc++")
 
+o("cflags", "llvm.cflags", "build LLVM with these extra compiler flags")
+o("cxxflags", "llvm.cxxflags", "build LLVM with these extra compiler flags")
+o("ldflags", "llvm.ldflags", "build LLVM with these extra linker flags")
+
 # Optimization and debugging options. These may be overridden by the release
 # channel, etc.
 o("optimize", "rust.optimize", "build optimized rust code")

src/bootstrap/native.rs

@@ -358,7 +358,11 @@ fn configure_cmake(builder: &Builder,
     }
 
     cfg.build_arg("-j").build_arg(builder.jobs().to_string());
-    cfg.define("CMAKE_C_FLAGS", builder.cflags(target, GitRepo::Llvm).join(" "));
+    let mut cflags = builder.cflags(target, GitRepo::Llvm).join(" ");
+    if let Some(ref s) = builder.config.llvm_cxxflags {
+        cflags.push_str(&format!(" {}", s));
+    }
+    cfg.define("CMAKE_C_FLAGS", cflags);
     let mut cxxflags = builder.cflags(target, GitRepo::Llvm).join(" ");
     if builder.config.llvm_static_stdcpp &&
         !target.contains("windows") &&
@@ -366,6 +370,9 @@ fn configure_cmake(builder: &Builder,
     {
         cxxflags.push_str(" -static-libstdc++");
     }
+    if let Some(ref s) = builder.config.llvm_cxxflags {
+        cxxflags.push_str(&format!(" {}", s));
+    }
     cfg.define("CMAKE_CXX_FLAGS", cxxflags);
     if let Some(ar) = builder.ar(target) {
         if ar.is_absolute() {
@@ -383,6 +390,12 @@ fn configure_cmake(builder: &Builder,
         }
     }
 
+    if let Some(ref s) = builder.config.llvm_ldflags {
+        cfg.define("CMAKE_SHARED_LINKER_FLAGS", s);
+        cfg.define("CMAKE_MODULE_LINKER_FLAGS", s);
+        cfg.define("CMAKE_EXE_LINKER_FLAGS", s);
+    }
+
     if env::var_os("SCCACHE_ERROR_LOG").is_some() {
         cfg.env("RUST_LOG", "sccache=warn");
     }