rust: fix compilation for Mountain Lion/clang 4.0

Closes Homebrew/homebrew#14457.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/rust.rb

@@ -10,8 +10,16 @@ class Rust < Formula
     cause "cannot initialize a parameter of type 'volatile long long *' with an rvalue of type 'int *'"
   end
 
+  def patches
+    # fix for Mountain Lion's clang 4.0
+    # should be part of next release (commit 50f2db4)
+    DATA
+  end
+
   def install
-    system "./configure", "--prefix=#{prefix}"
+    args = ["--prefix=#{prefix}"]
+    args << "--enable-clang" if ENV.compiler == :clang
+    system "./configure", *args
     system "make"
     system "make install"
   end
@@ -22,3 +30,18 @@ class Rust < Formula
     system "#{bin}/cargo"
   end
 end
+
+__END__
+diff --git a/configure b/configure
+index 06bddcc..040bae9 100755
+--- a/configure
++++ b/configure
+@@ -400,7 +400,7 @@ then
+                       | cut -d ' ' -f 2)
+
+     case $CFG_CLANG_VERSION in
+-        (3.0svn | 3.0 | 3.1)
++        (3.0svn | 3.0 | 3.1 | 4.0)
+         step_msg "found ok version of CLANG: $CFG_CLANG_VERSION"
+         CFG_C_COMPILER="clang"
+         ;;