Bug 1773223 - Turn gn into local toolchains. r=firefox-build-system-reviewers,ahochheiden a=RyanVM

- Because we don't have a native arm64 mac one, alias the x86_64 one.
- Because we always compress with zstd, don't pretend the main script
  has any power on the compression (which was wrong for Windows).

Differential Revision: https://phabricator.services.mozilla.com/D149204

taskcluster/ci/toolchain/gn.yml

@@ -4,11 +4,11 @@
 ---
 job-defaults:
     description: "gn toolchain build"
+    attributes:
+        local-toolchain: true
     worker-type: b-linux
     worker:
         max-run-time: 1800
-    run-on-projects:
-        - trunk
     run:
         resources:
             - 'taskcluster/scripts/misc/build-gn-common.sh'
@@ -28,6 +28,7 @@ macosx64-gn:
         symbol: TM(gn)
     run:
         script: build-gn-macosx.sh
+        toolchain-alias: macosx64-aarch64-gn
     fetches:
         toolchain:
             - linux64-cctools-port

taskcluster/scripts/misc/build-gn-common.sh

@@ -32,5 +32,5 @@ if test "$MAC_CROSS" = "" -a "$(uname)" = "Linux"; then
 fi
 cp out/gn $STAGE
 
-tar -c $STAGE | python3 $GECKO_PATH/taskcluster/scripts/misc/zstdpy > gn.tar.$COMPRESS_EXT
-cp gn.tar.$COMPRESS_EXT $UPLOAD_DIR
+tar -c $STAGE | python3 $GECKO_PATH/taskcluster/scripts/misc/zstdpy > gn.tar.zst
+cp gn.tar.zst $UPLOAD_DIR

taskcluster/scripts/misc/build-gn-linux.sh

@@ -4,7 +4,6 @@ set -e -v
 # This script is for building GN on Linux.
 
 WORKSPACE=$HOME/workspace
-COMPRESS_EXT=zst
 export CC=gcc
 export CXX=g++
 export LDFLAGS=-lrt

taskcluster/scripts/misc/build-gn-macosx.sh

@@ -4,7 +4,6 @@ set -e -v
 # This script is for building GN.
 
 WORKSPACE=$HOME/workspace
-COMPRESS_EXT=zst
 
 CROSS_CCTOOLS_PATH=$MOZ_FETCHES_DIR/cctools
 CROSS_SYSROOT=$MOZ_FETCHES_DIR/MacOSX11.0.sdk

taskcluster/scripts/misc/build-gn-win64.sh

@@ -4,7 +4,6 @@ set -e -v -x
 # This script is for building GN on Windows.
 
 UPLOAD_DIR=$PWD/public/build
-COMPRESS_EXT=bz2
 
 cd $GECKO_PATH