Add CLANG_BUILD_TOOLS as a clang counterpart for LLVM_BUILD_TOOLS

LLVM_BUILD_TOOLS is a boolean variable that controls whether or not generated
targets for llvm tools are built by the "all" target. CLANG_BUILD_TOOLS is an
analogous variable for clang targets.

This is useful functionality for selectively disabling the building of clang
targets by default to speed up builds.

In terms of implementation, I just followed the model of LLVM's implementation
of this functionality.

llvm-svn: 275006
diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 1a37b64..cfcd221 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -342,6 +342,9 @@
 
 add_definitions( -D_GNU_SOURCE )
 
+option(CLANG_BUILD_TOOLS
+  "Build the Clang tools. If OFF, just generate build targets." ON)
+
 option(CLANG_ENABLE_ARCMT "Build ARCMT." ON)
 if (CLANG_ENABLE_ARCMT)
   set(ENABLE_CLANG_ARCMT "1")