Add --enable-pgo option to build clang with PGO

tools/clang/CMakeLists.txt

Index: tools/clang/CMakeLists.txt
diff --git a/tools/clang/CMakeLists.txt b/tools/clang/CMakeLists.txt
index addcb5645183cebe3aa7519973914c223184bdf8..96ec29aaba55ccb281ac17db8ecbce3a9081933d 100644
--- a/tools/clang/CMakeLists.txt
+++ b/tools/clang/CMakeLists.txt
@@ -58,6 +58,11 @@ endfunction(cr_install)
 add_custom_target(cr-install COMMAND
   ${CMAKE_COMMAND} -D COMPONENT=chrome-tools -P cmake_install.cmake)
 
-foreach(tool ${CHROMIUM_TOOLS})
-  add_subdirectory(${tool})
-endforeach(tool)
+if (CHROMIUM_TOOLS)

[Nico, 2017/04/07 15:58:53]

why this change? seems independent of the rest of the patch (?)

[matthewtff.asm, 2017/04/11 12:14:43]

We do not pass -DBOOTSTRAP_CHROMIUM_TOOLS to cmake,
so it fails to build instrumented clang(which is between bootstrapped clang and
stage2 clang).

+  # CHROMIUM_TOOLS are separated by comma. To make it iterable cmake list
+  # replace those with semicolon.
+  string(REPLACE "," ";" CHROMIUM_TOOLS_LIST ${CHROMIUM_TOOLS})
+  foreach(tool ${CHROMIUM_TOOLS_LIST})
+    add_subdirectory(${tool})
+  endforeach(tool)
+endif(CHROMIUM_TOOLS)