Roll GN from 64b846c9 to 81ee1967.

https://gn.googlesource.com/gn.git/+log/64b846c9..81ee1967

81ee1967 Fix recursion on io_conversion help directions
73e89074 [docs] Fix typo 'is' => 'it'
f5ad8072 [docs] Use variable 'include_dirs' instead of 'includes‘
252674db Let source_target_relative be a valid substitution for bundle_data.
be0c06cb [infra] Switch to older Clang
9bd94208 Properly exit when an unknown tool is defined.
9a469b22 Refactor SubstitutionType for increased flexibility
19f79dec Add test for empty source set/static lib to NinjaBinaryTargetWriter
c599fdbb Fix use of 'is' operator for comparison
a4026b74 [infra] Delete cq.cfg
cf4c0734 [infra] Update recipes engine to 0589a4
d409ab89 Fix gn meta to handle non-string metadata
72a485f0 Remove check for C/C++ files on binary writer
9a3779dc Add support for .rs and .go source files
9ef31762 Move C logic to child class of NinjaBinaryTargetWriter
5b0bb6a7 Move Tool logic out of Toolchain
2691ec86 Canonicalize metadata walk_keys list before comaparing.
78db9de5 Fix formatting of escaping table.
cd8d9d47 Optimize string escape functions
2c72317e Support for building on OpenBSD.
2349dc4e [compdb] Optionally filter the compilation database.
0f3dbca6 Use LLVM archiver on macOS

Bug: gn:68, gn:67, gn:74, gn:77
Bug: chromium:958874, chromium:955936, chromium:608382
Change-Id: I79a25f6ad8e6656bc8d189821ac8311185868156
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616996
Auto-Submit: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661223}
diff --git a/DEPS b/DEPS
index 13a5b12..9b352ea4 100644
--- a/DEPS
+++ b/DEPS
@@ -287,7 +287,7 @@
   # revisions.
 
   # GN CIPD package version.
-  'gn_version': 'git_revision:64b846c96daeb3eaf08e26d8a84d8451c6cb712b',
+  'gn_version': 'git_revision:81ee1967d3fcbc829bac1c005c3da59739c88df9',
 
   # Also, if you change these, update buildtools/DEPS too. Also update the
   # libc++ svn_revision in //buildtools/deps_revisions.gni.
diff --git a/buildtools/DEPS b/buildtools/DEPS
index 55313b8..218a4fe 100644
--- a/buildtools/DEPS
+++ b/buildtools/DEPS
@@ -14,7 +14,7 @@
   #
 
   # GN CIPD package version.
-  'gn_version': 'git_revision:64b846c96daeb3eaf08e26d8a84d8451c6cb712b',
+  'gn_version': 'git_revision:81ee1967d3fcbc829bac1c005c3da59739c88df9',
 
   # When changing these, also update the svn revisions in deps_revisions.gni
   'clang_format_revision': '96636aa0e9f047f17447f2d45a094d0b59ed7917',