Cirrus-CI: add gcc12 automatic task on primary GitHub mirror

We want to get GCC coverage via Cirrus-CI, but don't want to trigger
excessive runs across all forks and branches.  Create a duplicate gcc12
task to run automatically for freebsd/freebsd-src.

Reviewed by:	jhb
Sponsored by:	The FreeBSD Foundation

.cirrus.yml

@@ -26,12 +26,18 @@ task:
       TARGET: arm64
       TARGET_ARCH: aarch64
       TOOLCHAIN_PKG: llvm15
-  - name: World and kernel gcc12 amd64 build and boot smoke test
+  - name: World and kernel gcc12 amd64 build and boot smoke test (manual)
     trigger_type: manual
     env:
       TARGET: amd64
       TARGET_ARCH: amd64
       TOOLCHAIN_PKG: amd64-gcc12
+  - name: World and kernel gcc12 amd64 build and boot smoke test (FreeBSD repo)
+    only_if: $CIRRUS_REPO_FULL_NAME == 'freebsd/freebsd-src'
+    env:
+      TARGET: amd64
+      TARGET_ARCH: amd64
+      TOOLCHAIN_PKG: amd64-gcc12
   timeout_in: 120m
   install_script:
   - sh .cirrus-ci/pkg-install.sh ${TOOLCHAIN_PKG} git-lite