Make all of the tools build in parallel. Missing this caused incremental
rebuilds to serially link each tool, which is really really slow.

We still have to build libclang serially first because c-index-test
depends on it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161612 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/Makefile b/tools/Makefile
index e7aa2fa..0bae772 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -11,10 +11,13 @@
 
 include $(CLANG_LEVEL)/../../Makefile.config
 
-DIRS := driver libclang c-index-test arcmt-test c-arcmt-test diagtool \
-        clang-check
+# Build libclang first so that other tools can depend on it.
+DIRS := libclang
+
+PARALLEL_DIRS := driver c-index-test arcmt-test c-arcmt-test diagtool \
+								 clang-check
 
 # Recurse into the extra repository of tools if present.
-OPTIONAL_DIRS := extra
+PARALLEL_OPTIONAL_DIRS := extra
 
 include $(CLANG_LEVEL)/Makefile