Reland "Roll GN from 81ee1967 to 8c7f4910"

This reverts commit 47efe3b5.

Reason for revert: Necessary CL possibly rolled into src-internal

Original change's description:
> Revert "Roll GN from 81ee1967 to 8c7f4910"
>
> This reverts commit 221c6f3d.
>
> Reason for revert: ChromeOS build failures; see https://crbug.com/974835.
>
> Original change's description:
> > Roll GN from 81ee1967 to 8c7f4910
> >
> > https://gn.googlesource.com/gn.git/+log/81ee1967..8c7f4910
> >
> > 8c7f491 rust: fix build on older clang by Tomasz Śniatowski
> > 8f8178c Escape prerequisites filenames in build.ninja.d depfile by samogot
> > 89d5ef5 Minor fixes to tracing by Julie Hockett
> > ae93998 An example Rust build by Julie Hockett
> > 80a5dc0 Ninja rules for Rust by Julie Hockett
> > e906492 Rust GN target generation by Julie Hockett
> > 586b028 Rust compilation tool and toolchain support by Julie Hockett
> > ed8b690 rust_library and Rust-specific variables by Julie Hockett
> > 5b16fb9 Rust substitutions and config values by Julie Hockett
> > b89110a Move SourceFileTypeSet to Target by Julie Hockett
> > 95a92a9 [espace.h] fix comment by Takuto Ikuta
> > 17cc456 json_project_writer: Output response_file_contents for action and action_for_each by Kimmo Kinnunen
> > 36c66bf Add additional surce files and example the list of acceptable files by Julie Hockett
> > 04f5df5 [args] Fix gn args unstable output by Haowei Wu
> > bc3fe2a [gen.py] Use relative -I switches and source paths by Roland McGrath
> > 8730b0f Disallow non-buildable sources in binary targets by Tom Anderson
> > 0d038c2 Cache source file type in SourceFile by Tom Anderson
> >
> > BUG=964411
> > R=​dpranke
> >
> > Change-Id: Ib9ea522a075fba2ca81b91ab347731a7829901b9
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1650093
> > Reviewed-by: Nico Weber <thakis@chromium.org>
> > Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> > Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#669546}
>
> TBR=thakis@chromium.org,dpranke@chromium.org,thomasanderson@chromium.org
>
> Change-Id: Icf28406f4f204a5814cbd0d305f2508240df0dc5
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 964411
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660809
> Reviewed-by: Sidney San Martín <sdy@chromium.org>
> Commit-Queue: Sidney San Martín <sdy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#669716}

TBR=thakis@chromium.org,dpranke@chromium.org,xiaohuic@chromium.org,sdy@chromium.org,thomasanderson@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

TBR=dpranke

Bug: 964411
Change-Id: I6918691612d8f4aa3899aa3b2ecf6b3f9e5c02fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1664207
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671388}

DEPS

@@ -292,7 +292,7 @@ vars = {
   # revisions.
 
   # GN CIPD package version.
-  'gn_version': 'git_revision:81ee1967d3fcbc829bac1c005c3da59739c88df9',
+  'gn_version': 'git_revision:8c7f49102234f4f4b9349dcb258554675475e596',
 
   # 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:81ee1967d3fcbc829bac1c005c3da59739c88df9',
+  'gn_version': 'git_revision:8c7f49102234f4f4b9349dcb258554675475e596',
 
   # When changing these, also update the svn revisions in deps_revisions.gni
   'clang_format_revision': '96636aa0e9f047f17447f2d45a094d0b59ed7917',