Pull buildtools to get GN 296277

TBR=scottmg

Review URL: https://codereview.chromium.org/593333002

Cr-Commit-Position: refs/heads/master@{#296313}

DEPS

@@ -55,7 +55,7 @@ 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': 'ac93c78aa1a5b1c5fe5ce01abb3063d750aaf2f3',
+  'buildtools_revision': '6d24aadb361dc9a914bbe321915972461fe0444c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFIum
   # and whatever else without interference from each other.