Ports: Port gn

This requires allowing ports to override fetch() since tar.gz sha256sums
from googlesource.com are not deterministic.

Ports/gn/package.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port='gn'
+workdir='gn'
+version='2023.07.12'
+repository='https://gn.googlesource.com/gn'
+git_rev='fae280eabe5d31accc53100137459ece19a7a295'
+useconfigure='true'
+# FIXME: The files and auth_type are lies here. See #20004
+files=('git')
+auth_type='sha256'
+depends=(
+    'ninja'
+    'python3'
+)
+
+fetch() {
+    if [ ! -d ${workdir} ]; then
+        git clone ${repository} ${workdir}
+    fi
+    run git checkout ${git_rev}
+}
+
+configure() {
+    run python3 build/gen.py --platform='serenity' --allow-warnings
+}
+
+build() {
+    run ninja -C out
+}
+
+install() {
+    run mkdir -p "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+    run cp out/gn "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+    run cp out/gn_unittests "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+}