[autotools->cmake] Added support for building clang with an order file.

llvm-svn: 188763

clang/CMakeLists.txt

@@ -337,3 +337,6 @@ endif()
 
 set(BUG_REPORT_URL "http://llvm.org/bugs/" CACHE STRING
   "Default URL where bug reports are to be submitted.")
+
+option(CLANG_ORDER_FILE
+  "Order file to use when compiling clang in order to improve startup time." "")

clang/tools/driver/CMakeLists.txt

@@ -116,3 +116,8 @@ if (APPLE)
   set(TOOL_INFO_VERSION)
   set(TOOL_INFO_BUILD_VERSION)
 endif()
+
+if(CLANG_ORDER_FILE)
+  target_link_libraries(clang "-Wl,-order_file,${CLANG_ORDER_FILE}")
+endif()
+