Roll DEPS for buildtools to 5fd66957f0.

DEPS

 use_relative_paths = True
 
 vars = {
   'chromium_git': 'https://chromium.googlesource.com',
   'pdfium_git': 'https://pdfium.googlesource.com',
 
   'android_ndk_revision': '5022f40f12953c02b2614c5f7beb981ec5d0e833',
   'build_revision': 'b73bafdd0ff0efc8835de6e646b47eec0a2a38a4',
-  'buildtools_revision': 'adb8bf4e8fc92aa1717bf151b862d58e6f27c4f2',
+  'buildtools_revision': '5fd66957f08bb752dca714a591c84587c9d70762',
   'catapult_revision': '327256cb1c387e62a2c7e6960e2398867665fb51',
   'clang_revision': '797371be0a75c9892d6acb486d0430915ea538a6',
   'cygwin_revision': 'c89e446b273697fadf3a10ff1007a97c0b7de6df',
   'gen_library_loader_revision': '916d4acd8b2cde67a390737dfba90b3c37de23a1',
   'gmock_revision': '29763965ab52f24565299976b936d1265cb6a271',
   'gtest_revision': '8245545b6dc9c4703e6496d1efd19e975ad2b038',
   'icu_revision': '2341038bf72869a5683a893a2b319a48ffec7f62',
   'pdfium_tests_revision': 'e86a1bac556194ee572b0cd37d04ea646c7b5320',
   'skia_revision': '39f7a10a04a914384944d8bf62621144ac4eeaa3',
   'tools_memory_revision': '427f10475e1a8d72424c29d00bf689122b738e5d',
@@ skipping 52 matching lines @@
       Var('chromium_git') + "/android_ndk.git@" + Var('android_ndk_revision'),
     "third_party/catapult":
       Var('chromium_git') + "/external/github.com/catapult-project/catapult.git@" + Var('catapult_revision'),
   },
   "win": {
     "v8/third_party/cygwin":
       Var('chromium_git') + "/chromium/deps/cygwin@" + Var('cygwin_revision'),
   },
 }
 
+recursedeps = [
+  # buildtools provides clang_format, libc++, and libc++abi
+  'buildtools',
+]
+
 include_rules = [
   # Basic stuff that everyone can use.
   # Note: public is not here because core cannot depend on public.
   '+testing',
   '+third_party/base',
 ]
 
 specific_include_rules = {
   # Allow embedder tests to use public APIs.
   "(.*embeddertest\.cpp)": [
@@ skipping 77 matching lines @@
                'pdfium/tools/clang/scripts/update.py'
     ],
   },
   {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'pdfium/build/vs_toolchain.py', 'update'],
   },
 ]