Roll GN from 6feb5599..a5bcbd72

    a5bcbd72 Update default VS to 2019
    ff241a58 Update Rust example to match modern gn needs.
    56246794 Fix quoting preprocessor defines for compilation database

Bug: 1038361
Change-Id: I74a864e0d4ec41bae0795353a30e2c032a580c14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1984714Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Auto-Submit: Aaron Gable <agable@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727848}

DEPS

@@ -337,7 +337,7 @@ vars = {
   # revisions.
 
   # GN CIPD package version.
-  'gn_version': 'git_revision:6feb55993083dfd27b93da195c8a82a3a9529848',
+  'gn_version': 'git_revision:a5bcbd726ac7bd342ca6ee3e3a006478fd1f00b5',
 
   # Also, if you change these, update buildtools/DEPS too. Also update the
   # libc++ svn_revision in //buildtools/deps_revisions.gni.

buildtools/DEPS

@@ -14,7 +14,7 @@ vars = {
   #
 
   # GN CIPD package version.
-  'gn_version': 'git_revision:6feb55993083dfd27b93da195c8a82a3a9529848',
+  'gn_version': 'git_revision:a5bcbd726ac7bd342ca6ee3e3a006478fd1f00b5',
 
   # When changing these, also update the svn revisions in deps_revisions.gni
   'clang_format_revision': '96636aa0e9f047f17447f2d45a094d0b59ed7917',