[llvm] [libcxx] [libc++] Trigger the buildkite CI only if stages 1 and 2 already passed (PR #79209)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 updated https://github.com/llvm/llvm-project/pull/79209

>From a1b7ef026f1c633d81b7f64ccac58f6137176f91 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Tue, 23 Jan 2024 21:54:38 +0100
Subject: [PATCH] [libc++] Trigger the buildkite CI only if stages 1 and 2
 already passed

---
 .ci/generate-buildkite-pipeline-premerge     | 11 -----------
 .github/workflows/libcxx-build-and-test.yaml | 10 ++++++++++
 libcxx/include/libcxx_trigger                |  0
 3 files changed, 10 insertions(+), 11 deletions(-)
 create mode 100644 libcxx/include/libcxx_trigger

diff --git a/.ci/generate-buildkite-pipeline-premerge b/.ci/generate-buildkite-pipeline-premerge
index f32eb7213b9402..318b968fbc7025 100755
--- a/.ci/generate-buildkite-pipeline-premerge
+++ b/.ci/generate-buildkite-pipeline-premerge
@@ -197,17 +197,6 @@ function check-targets() {
 
 # Project specific pipelines.
 
-# If libc++ or one of the runtimes directories changed.
-if echo "$modified_dirs" | grep -q -E "^(libcxx|libcxxabi|libunwind|runtimes|cmake)$"; then
-  cat <<EOF
-- trigger: "libcxx-ci"
-  build:
-    message: "${buildMessage}"
-    commit: "${BUILDKITE_COMMIT}"
-    branch: "${BUILDKITE_BRANCH}"
-EOF
-fi
-
 # If clang changed.
 if echo "$modified_dirs" | grep -q -E "^(clang)$"; then
   cat <<EOF
diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index 1666a687aa5d04..dd5b7302506cbd 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -207,3 +207,13 @@ jobs:
             **/CMakeError.log
             **/CMakeOutput.log
             **/crash_diagnostics/*
+  buildkite-stage:
+    if: github.repository_owner == 'llvm'
+    runs-on: ubuntu-latest
+    continue-on-error: false
+    steps:
+      - name: Trigger Buildkite Pipeline
+        uses: buildkite/trigger-pipeline-action at v2.0.0
+        with:
+          buildkite_api_access_token: ${{ secrets.TRIGGER_BK_BUILD_TOKEN }}
+          pipeline: "llvm-project/libcxx-ci"
diff --git a/libcxx/include/libcxx_trigger b/libcxx/include/libcxx_trigger
new file mode 100644
index 00000000000000..e69de29bb2d1d6