//build/vs_toolchain.py: Fix SyntaxWarnings about invalid escape sequences

Warnings when running "gn gen" on Python 3.8:
C:/Google/chromium/src/build/vs_toolchain.py:257: SyntaxWarning: invalid escape sequence \.
  if re.match('10\.\d+\.\d+\.\d+', directory):
C:/Google/chromium/src/build/vs_toolchain.py:281: SyntaxWarning: invalid escape sequence \.
  if re.match('14\.\d+\.\d+', directory):
C:/Google/chromium/src/build/vs_toolchain.py:257: SyntaxWarning: invalid escape sequence \.
  if re.match('10\.\d+\.\d+\.\d+', directory):
C:/Google/chromium/src/build/vs_toolchain.py:281: SyntaxWarning: invalid escape sequence \.
  if re.match('14\.\d+\.\d+', directory):
C:/Google/chromium/src/build/toolchain/win\..\..\vs_toolchain.py:257: SyntaxWarning: invalid escape sequence \.
  if re.match('10\.\d+\.\d+\.\d+', directory):
C:/Google/chromium/src/build/toolchain/win\..\..\vs_toolchain.py:281: SyntaxWarning: invalid escape sequence \.
  if re.match('14\.\d+\.\d+', directory):

Bug: 941669
Change-Id: I2ab9fc1e404c2bdeba606c6391f8ac8149d92e62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585889Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Raul Tambre <raul@tambre.ee>
Auto-Submit: Raul Tambre <raul@tambre.ee>
Cr-Commit-Position: refs/heads/master@{#654764}

build/vs_toolchain.py

@@ -254,7 +254,7 @@ def _CopyUCRTRuntime(target_dir, source_dir, target_cpu, dll_pattern, suffix):
         sdk_redist_root_version = os.path.join(sdk_redist_root, directory)
         if not os.path.isdir(sdk_redist_root_version):
           continue
-        if re.match('10\.\d+\.\d+\.\d+', directory):
+        if re.match(r'10\.\d+\.\d+\.\d+', directory):
           source_dir = os.path.join(sdk_redist_root_version, target_cpu, 'ucrt')
           break
     _CopyRuntimeImpl(os.path.join(target_dir, 'ucrtbase' + suffix),
@@ -278,7 +278,7 @@ def FindVCComponentRoot(component):
   for directory in vc_component_msvc_contents:
     if not os.path.isdir(os.path.join(vc_component_msvc_root, directory)):
       continue
-    if re.match('14\.\d+\.\d+', directory):
+    if re.match(r'14\.\d+\.\d+', directory):
       return os.path.join(vc_component_msvc_root, directory)
   raise Exception('Unable to find the VC %s directory.' % component)