[libc++][hardening] Make the safe mode pipeline run with modules enabled

Differential Revision: https://reviews.llvm.org/D159065

Author: var-const

libcxx/cmake/caches/Generic-safe-mode.cmake

@@ -1 +1,2 @@
+set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_HARDENING_MODE "safe" CACHE STRING "")

libcxx/utils/ci/buildkite-pipeline.yml

@@ -505,8 +505,11 @@ steps:
       - "**/test-results.xml"
       - "**/*.abilist"
     env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
+        # Note: Modules require an absolute path for `clang-scan-deps` (see
+        # 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"