Add support for downloading clang

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 81344e97a0e284be1739d5465fc53e516740e659..fb9433ca8a6395e3bf5121f5f3a0b735c076c08f 100644
--- a/DEPS
+++ b/DEPS
@@ -18,6 +18,8 @@ deps = {
     Var("git_url") + "/external/googletest.git@4650552ff637bb44ecf7784060091cbed3252211",
   "v8/testing/gmock":
     Var("git_url") + "/external/googlemock.git@896ba0e03f520fb9b6ed582bde2bd00847e3c3f2",
+  "v8/tools/clang":
+    Var("git_url") + "/chromium/src/tools/clang.git@327e26ee7f6ae6f86fb335113b46cb86ed3cb0dc",

[Michael Achenbach, 2014/11/26 15:08:34]

Be aware of make dependencies...

[jochen (gone - plz use gerrit), 2014/11/27 10:02:39]

everybody should be using gclient sync, no?

[Michael Achenbach, 2014/11/27 10:13:05]

I can't speak for other people. The best way to enforce that is to remove the
dependencies target from the Makefile. I'll do that and wait for complaints...

 }
 
 deps_os = {
@@ -82,6 +84,13 @@ hooks = [
     ],
   },
   {
+    # Pull clang if needed or requested via GYP_DEFINES.

[Michael Achenbach, 2014/11/26 15:08:34]

I don't understand how this is dependent on GYP_DEFINES. Is the update script
only called if clang=1 or always?

[jochen (gone - plz use gerrit), 2014/11/27 10:02:39]

it internally checks the gyp defines

+    # Note: On Win, this should run after win_toolchain, as it may use it.
+    'name': 'clang',
+    'pattern': '.',
+    'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
+  },
+  {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "v8/build/gyp_v8"],