[libc++][CI] Allow retries in case an agent is lost

We see this fairly often on our Linux bots, which appear to be killed
by GCE from time to time.

libcxx/utils/ci/buildkite-pipeline.yml

@@ -21,132 +21,208 @@ steps:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "C++11"
     command: "libcxx/utils/ci/run-buildbot.sh generic-cxx11"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "C++14"
     command: "libcxx/utils/ci/run-buildbot.sh generic-cxx14"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "C++17"
     command: "libcxx/utils/ci/run-buildbot.sh generic-cxx17"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "C++20"
     command: "libcxx/utils/ci/run-buildbot.sh generic-cxx2a"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "-fno-exceptions"
     command: "libcxx/utils/ci/run-buildbot.sh generic-noexceptions"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "GCC/C++20"
     command: "libcxx/utils/ci/run-buildbot.sh generic-gcc"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "ASAN"
     command: "libcxx/utils/ci/run-buildbot.sh generic-asan"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "TSAN"
     command: "libcxx/utils/ci/run-buildbot.sh generic-tsan"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "UBSAN"
     command: "libcxx/utils/ci/run-buildbot.sh generic-ubsan"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "With LLVM's libunwind"
     command: "libcxx/utils/ci/run-buildbot.sh generic-with_llvm_unwinder"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "Single-threaded"
     command: "libcxx/utils/ci/run-buildbot.sh generic-singlethreaded"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "No debug mode"
     command: "libcxx/utils/ci/run-buildbot.sh generic-nodebug"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "No random device"
     command: "libcxx/utils/ci/run-buildbot.sh generic-no-random_device"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "No locale"
     command: "libcxx/utils/ci/run-buildbot.sh generic-no-localization"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "MacOS C++20"
     command: "libcxx/utils/ci/run-buildbot.sh generic-cxx2a"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-macos-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "Benchmarks"
     command: "libcxx/utils/ci/run-buildbot.sh benchmarks"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "Legacy standalone build"
     command: "libcxx/utils/ci/run-buildbot.sh legacy-standalone"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "Unified standalone build"
     command: "libcxx/utils/ci/run-buildbot.sh unified-standalone"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   # Build with the configuration we use to generate libc++.dylib on Apple platforms
   - label: "Apple system"
@@ -155,10 +231,18 @@ steps:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-macos-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
 
   - label: "Apple system -fno-exceptions"
     command: "libcxx/utils/ci/run-buildbot.sh x86_64-apple-system-noexceptions"
     artifact_paths:
       - "**/test-results.xml"
     agents:
       queue: "libcxx-macos-builders"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2