Revert of Roll buildtools aa47d9773d..924d50ecae (patchset #1 id:1 of...

Revert of Roll buildtools aa47d9773d..924d50ecae (patchset #1 id:1 of https://codereview.chromium.org/2138013004/ )

Reason for revert:
Broke uses of 'clang=1 llvm_force_head_revision=1' on clang tot waterfall:
https://build.chromium.org/p/chromium.fyi/console?category=clang%20tot

Original issue's description:
> Roll buildtools aa47d9773d..924d50ecae
>
>   In order to roll GN b9999d69..4828a631 (r403866:r404813) and pick up
>   the following changes:
>
>   5662a808 GN: Don't define argument overrides globally
>   45a841b0 Suggest `gn help` for internally set arguments.
>   bf462ea0 [GN docs] Add missing word in gn actions help string
>   8273381e Fix typos in GN error message
>
> TBR=dpranke@chromium.org
>
> Committed: https://crrev.com/932788e86f1f59cdff52df8ae78784af6f8a17e6
> Cr-Commit-Position: refs/heads/master@{#405054}

TBR=dpranke@chromium.org,brettw@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2146023002
Cr-Commit-Position: refs/heads/master@{#405169}

DEPS

@@ -52,7 +52,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.
-  'buildtools_revision': '924d50ecaeb08f1baf52aa9e032895cedcd3238a',
+  'buildtools_revision': 'aa47d9773d8f4d6254a587a1240b3dc023d54f06',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.