Use Clang's update.py --print-revision everywhere.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 1284360f9a3a8ba9fe69f8a79bcb1b70cad421db..23e1b443dbab683a92319e2e0af3f5278bc8de9e 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -2625,13 +2625,13 @@
           ],
         },
       }],
-      ['(clang==1 or host_clang==1) and OS!="win"', {
+      ['clang==1 or host_clang==1', {
         # This is here so that all files get recompiled after a clang roll and
         # when turning clang on or off.
         # (defines are passed via the command line, and build systems rebuild
         # things when their commandline changes). Nothing should ever read this
         # define.
-        'defines': ['CR_CLANG_REVISION=<!(<(DEPTH)/tools/clang/scripts/update.sh --print-revision)'],
+        'defines': ['CR_CLANG_REVISION=<!(python <(DEPTH)/tools/clang/scripts/update.py --print-revision)'],
       }],
       ['enable_rlz==1', {
         'defines': ['ENABLE_RLZ'],