[libc++][CI] Tests the no RTTI configuration.

There are a few drive-by fixes:
- Since the combination RTTI disabled and exceptions enabled do not
  work, this combination is prohibited.
- A small NFC in any fixing clang-tidy.

The code in the Buildkite configuration is prepared for using the std
module. There are more fixes needed for that configuration which will be
done in a separate commit.

Author: mordante

libcxx/CMakeLists.txt

@@ -279,7 +279,9 @@ endif()
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_ENABLE_EXCEPTIONS "Use exceptions." ON)
-option(LIBCXX_ENABLE_RTTI "Use run time type information." ON)
+option(LIBCXX_ENABLE_RTTI
+  "Use run time type information.
+   This option may only be set to OFF when LIBCXX_ENABLE_EXCEPTIONS=OFF." ON)
 option(LIBCXX_ENABLE_THREADS "Build libc++ with support for threads." ON)
 option(LIBCXX_ENABLE_MONOTONIC_CLOCK
   "Build libc++ with support for a monotonic clock.
@@ -370,6 +372,11 @@ if (LIBCXX_HAS_PTHREAD_API)
   endif()
 endif()
 
+if (NOT LIBCXX_ENABLE_RTTI AND LIBCXX_ENABLE_EXCEPTIONS)
+  message(FATAL_ERROR "The option LIBCXX_ENABLE_RTTI can not be turned off"
+	                  " when LIBCXX_ENABLE_EXCEPTIONS is turned on.")
+endif()
+
 # Ensure LLVM_USE_SANITIZER is not specified when LIBCXX_GENERATE_COVERAGE
 # is ON.
 if (LLVM_USE_SANITIZER AND LIBCXX_GENERATE_COVERAGE)

libcxx/cmake/caches/Generic-no-rtti.cmake

@@ -0,0 +1,4 @@
+set(LIBCXX_ENABLE_RTTI OFF CACHE BOOL "")
+set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+set(LIBCXXABI_ENABLE_RTTI OFF CACHE BOOL "")
+set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")

libcxx/docs/BuildingLibcxx.rst

@@ -378,6 +378,7 @@ libc++ Feature Options
   **Default**: ``ON``
 
   Build libc++ with run time type information.
+  This option may only be set to OFF when LIBCXX_ENABLE_EXCEPTIONS=OFF.
 
 .. option:: LIBCXX_INCLUDE_TESTS:BOOL
 

libcxx/include/any

@@ -196,9 +196,7 @@ namespace __any_imp
       if (__id && *__id == typeid(_Tp))
           return true;
 #endif
-      if (!__id && __fallback_id == __any_imp::__get_fallback_typeid<_Tp>())
-          return true;
-      return false;
+      return !__id && __fallback_id == __any_imp::__get_fallback_typeid<_Tp>();
   }
 
   template <class _Tp>

libcxx/utils/ci/buildkite-pipeline.yml

@@ -741,6 +741,27 @@ steps:
             limit: 2
       timeout_in_minutes: 120
 
+    - label: "No RTTI"
+      command: "libcxx/utils/ci/run-buildbot generic-no-rtti"
+      artifact_paths:
+        - "**/test-results.xml"
+        - "**/*.abilist"
+      env:
+          # Note: Modules require and absolute path for clang-scan-deps
+          # https://github.com/llvm/llvm-project/issues/61006
+          CC: "/usr/lib/llvm-${LLVM_HEAD_VERSION}/bin/clang"
+          CXX: "/usr/lib/llvm-${LLVM_HEAD_VERSION}/bin/clang++"
+          CMAKE: "/opt/bin/cmake"
+          ENABLE_CLANG_TIDY: "On"
+      agents:
+        queue: "libcxx-builders"
+        os: "linux"
+      retry:
+        automatic:
+          - exit_status: -1  # Agent was lost
+            limit: 2
+      timeout_in_minutes: 120
+
   - label: "Unstable ABI"
     command: "libcxx/utils/ci/run-buildbot generic-abi-unstable"
     artifact_paths:

libcxx/utils/ci/run-buildbot

@@ -476,6 +476,11 @@ generic-no-exceptions)
     check-runtimes
     check-abi-list
 ;;
+generic-no-rtti)
+    clean
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-no-rtti.cmake"
+    check-runtimes
+;;
 #
 # Other miscellaneous jobs
 #