Improved checking of target's llvm_config

Point llvm @bitshifter branch until PR accepted

Use today's date for LLVM auto clean trigger

Update LLVM submodule to point at rust-lang fork.

Handle case when target is set

src/bootstrap/compile.rs

@@ -199,7 +199,7 @@ pub fn rustc<'a>(build: &'a Build, target: &str, compiler: &Compiler<'a>) {
         cargo.env("CFG_DISABLE_UNSTABLE_FEATURES", "1");
     }
     // Flag that rust llvm is in use
-    if build.config.target_config.get(target).is_none() {
+    if build.is_rust_llvm(target) {
         cargo.env("LLVM_RUSTLLVM", "1");
     }
     cargo.env("LLVM_CONFIG", build.llvm_config(target));

src/bootstrap/lib.rs

@@ -727,6 +727,16 @@ impl Build {
         self.out.join(target).join("llvm")
     }
 
+    /// Returns true if no custom `llvm-config` is set for the specified target.
+    ///
+    /// If no custom `llvm-config` was specified then Rust's llvm will be used.
+    fn is_rust_llvm(&self, target: &str) -> bool {
+        match self.config.target_config.get(target) {
+            Some(ref c) => c.llvm_config.is_none(),
+            None => true
+        }
+    }
+
     /// Returns the path to `llvm-config` for the specified target.
     ///
     /// If a custom `llvm-config` was specified for target then that's returned

src/rustllvm/llvm-auto-clean-trigger

@@ -1,4 +1,4 @@
 # If this file is modified, then llvm will be forcibly cleaned and then rebuilt.
 # The actual contents of this file do not matter, but to trigger a change on the
 # build bots then the contents should be changed so git updates the mtime.
-2016-07-25b
+2016-08-07