[runtimes] Reintroduce a way to select the compiler used for the test suite (#93542)

A while back, the cxx_under_test Lit parameter was removed. This patch
reintroduces a Lit parameter called "compiler" which controls the value
of the %{cxx} substitution used in the test suite.

To run the test suite with a different compiler, one can now pass
--param compiler=<path>.

libcxx/test/CMakeLists.txt

@@ -16,6 +16,8 @@ endif()
 set(AUTO_GEN_COMMENT "## Autogenerated by libcxx configuration.\n# Do not edit!")
 set(SERIALIZED_LIT_PARAMS "# Lit parameters serialized here for llvm-lit to pick them up\n")
 
+serialize_lit_string_param(SERIALIZED_LIT_PARAMS compiler "${CMAKE_CXX_COMPILER}")
+
 if (NOT LIBCXX_ENABLE_EXCEPTIONS)
   serialize_lit_param(SERIALIZED_LIT_PARAMS enable_exceptions False)
 endif()

libcxx/test/configs/cmake-bridge.cfg.in

@@ -23,8 +23,6 @@ config.recursiveExpansionLimit = 10
 config.test_exec_root = os.path.join('@CMAKE_BINARY_DIR@', 'test')
 
 # Add substitutions for bootstrapping the test suite configuration
-import shlex
-config.substitutions.append(('%{cxx}', shlex.quote('@CMAKE_CXX_COMPILER@')))
 config.substitutions.append(('%{libcxx-dir}', '@LIBCXX_SOURCE_DIR@'))
 config.substitutions.append(('%{include-dir}', '@LIBCXX_GENERATED_INCLUDE_DIR@'))
 config.substitutions.append(('%{target-include-dir}', '@LIBCXX_GENERATED_INCLUDE_TARGET_DIR@'))

libcxx/utils/libcxx/test/params.py

@@ -143,6 +143,14 @@ def getSuitableClangTidy(cfg):
 
 # fmt: off
 DEFAULT_PARAMETERS = [
+    Parameter(
+        name="compiler",
+        type=str,
+        help="The path of the compiler to use for testing.",
+        actions=lambda cxx: [
+            AddSubstitution("%{cxx}", shlex.quote(cxx)),
+        ],
+    ),
     Parameter(
         name="target_triple",
         type=str,

libcxxabi/test/CMakeLists.txt

@@ -24,6 +24,8 @@ endif()
 set(AUTO_GEN_COMMENT "## Autogenerated by libcxxabi configuration.\n# Do not edit!")
 set(SERIALIZED_LIT_PARAMS "# Lit parameters serialized here for llvm-lit to pick them up\n")
 
+serialize_lit_string_param(SERIALIZED_LIT_PARAMS compiler "${CMAKE_CXX_COMPILER}")
+
 if (NOT LIBCXXABI_ENABLE_EXCEPTIONS)
   serialize_lit_param(SERIALIZED_LIT_PARAMS enable_exceptions False)
 endif()

libcxxabi/test/configs/cmake-bridge.cfg.in

@@ -26,7 +26,6 @@ config.test_exec_root = os.path.join('@CMAKE_BINARY_DIR@', 'test')
 # TODO: This is a non-standard Lit attribute and we should have another way of accessing this.
 config.host_triple = '@LLVM_HOST_TRIPLE@'
 
-config.substitutions.append(('%{cxx}', '@CMAKE_CXX_COMPILER@'))
 config.substitutions.append(('%{libcxx}', '@LIBCXXABI_LIBCXX_PATH@'))
 config.substitutions.append(('%{include}', '@LIBCXXABI_SOURCE_DIR@/include'))
 config.substitutions.append(('%{cxx-include}', '@LIBCXXABI_HEADER_DIR@/include/c++/v1'))

libunwind/test/CMakeLists.txt

@@ -15,6 +15,8 @@ pythonize_bool(LIBUNWIND_USES_ARM_EHABI)
 set(AUTO_GEN_COMMENT "## Autogenerated by libunwind configuration.\n# Do not edit!")
 set(SERIALIZED_LIT_PARAMS "# Lit parameters serialized here for llvm-lit to pick them up\n")
 
+serialize_lit_string_param(SERIALIZED_LIT_PARAMS compiler "${CMAKE_CXX_COMPILER}")
+
 if (LIBUNWIND_EXECUTOR)
   message(DEPRECATION "LIBUNWIND_EXECUTOR is deprecated, please add executor=... to LIBUNWIND_TEST_PARAMS")
   serialize_lit_string_param(SERIALIZED_LIT_PARAMS executor "${LIBUNWIND_EXECUTOR}")

libunwind/test/configs/cmake-bridge.cfg.in

@@ -29,7 +29,5 @@ if not @LIBUNWIND_ENABLE_THREADS@:
     config.available_features.add('libunwind-no-threads')
 
 # Add substitutions for bootstrapping the test suite configuration
-import shlex
-config.substitutions.append(('%{cxx}', shlex.quote('@CMAKE_CXX_COMPILER@')))
 config.substitutions.append(('%{include}', '@LIBUNWIND_SOURCE_DIR@/include'))
 config.substitutions.append(('%{lib}', '@LIBUNWIND_LIBRARY_DIR@'))