[llvm] Point workflow yaml at new docker image (PR #133359)

[George Burgess IV via llvm-commits]

https://github.com/gburgessiv updated https://github.com/llvm/llvm-project/pull/133359

>From 03e97440389a7fedc0854cf6ca5c589bf45c5ba2 Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv at gmail.com>
Date: Thu, 27 Mar 2025 20:48:47 -0600
Subject: [PATCH 1/2] .github: rely on new llvm-project checkout

This is now baked into the docker images to speed up
premerge cycle times.
---
 .github/workflows/premerge.yaml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/premerge.yaml b/.github/workflows/premerge.yaml
index c315ee37646d2..33e874b5004a6 100644
--- a/.github/workflows/premerge.yaml
+++ b/.github/workflows/premerge.yaml
@@ -26,6 +26,11 @@ concurrency:
 jobs:
   premerge-checks-linux:
     name: Linux Premerge Checks (Test Only - Please Ignore Results)
+    defaults:
+      run:
+        # The premerge Linux docker instance keeps a pristine clone of LLVM in
+        # /home/gha/llvm-project; that should be used as our main workdir.
+        working-directory: /home/gha/llvm-project
     if: >-
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
@@ -34,7 +39,7 @@ jobs:
       - name: Checkout LLVM
         uses: actions/checkout at 11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          fetch-depth: 2
+          path: /home/gha/llvm-project
       - name: Setup ccache
         uses: hendrikmuhs/ccache-action at a1209f81afb8c005c13b4296c32e363431bffea5 # v1.2.17
         with:

>From 3a839f29e64a143103ed8b2cb08561aa0ef44aab Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv at gmail.com>
Date: Thu, 27 Mar 2025 20:49:39 -0600
Subject: [PATCH 2/2] DO NOT COMMIT: tweak premerge to use custom image

For help in testing the prior commit
---
 .github/workflows/premerge.yaml | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/.github/workflows/premerge.yaml b/.github/workflows/premerge.yaml
index 33e874b5004a6..3da671c5fdba0 100644
--- a/.github/workflows/premerge.yaml
+++ b/.github/workflows/premerge.yaml
@@ -26,20 +26,24 @@ concurrency:
 jobs:
   premerge-checks-linux:
     name: Linux Premerge Checks (Test Only - Please Ignore Results)
-    defaults:
-      run:
-        # The premerge Linux docker instance keeps a pristine clone of LLVM in
-        # /home/gha/llvm-project; that should be used as our main workdir.
-        working-directory: /home/gha/llvm-project
     if: >-
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
-    runs-on: llvm-premerge-linux-runners
     steps:
+      - name: Seed LLVM repo
+        run: |
+          # Github creates a directory at GITHUB_WORKSPACE by defualt; replace it
+          # with a symlink to our pre-checked-out LLVM repo (this is necessary
+          # since actions/checkout _really wants_ a path inside of
+          # `${GITHUB_WORKSPACE}`
+          rmdir "${GITHUB_WORKSPACE}"
+          ln -s /home/gha/llvm-project "${GITHUB_WORKSPACE}"
       - name: Checkout LLVM
         uses: actions/checkout at 11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          path: /home/gha/llvm-project
+          fetch-depth: 2
+          # This repo is frozen with the docker container; no need to clean.
+          clean: false
       - name: Setup ccache
         uses: hendrikmuhs/ccache-action at a1209f81afb8c005c13b4296c32e363431bffea5 # v1.2.17
         with: