[Interop][testing] Use libc++ from target Darwin SDK for clang check invocations

Author: hyp

test/lit.cfg

@@ -574,40 +574,6 @@ config.substitutions.append( ('%clang',
                               "%r %s" %
                                 (config.clang, clang_mcp_opt)) )
 
-extraCheckWarningFlags = (
-  # Turn on all warnings and promote them to errors
-  '-Weverything -Werror '
-  # Don't warn about unused macros in our clang header.
-  '-Wno-unused-macros '
-  # Don't warn about module imports used at #includes.
-  '-Wno-incomplete-module -Wno-auto-import '
-  # Don't warn about any variadic macros we might have.
-  '-Wno-variadic-macros '
-  # Don't warn about any C++98 compatibility issues.
-  '-Wno-c++98-compat-pedantic '
-  # Don't warn about poison system directories in the Linux system paths.
-  '-Wno-poison-system-directories '
-  # For -fmodules-cache-path, when modules are off.
-  '-Wno-unused-command-line-argument '
-  # Don't warn about nullability specifiers in C/C++ code.
-  '-Wno-nullability-extension ')
-
-# Verifies that a C++ file can be compiled without warnings except for some exceptions.
-config.substitutions.insert(0, ('%check-c-header-in-clang',
-  '%clang -fsyntax-only -x c-header ' + extraCheckWarningFlags +
-  # Use standard header/framework search paths.
-  '-F %%clang-importer-sdk-path/frameworks '
-  '-I %%clang-include-dir '
-  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
-
-# Verifies that a C++ file can be compiled without warnings except for some exceptions.
-config.substitutions.insert(0, ('%check-cxx-header-in-clang',
-  '%clangxx -fsyntax-only -x c++-header ' + extraCheckWarningFlags +
-  # Use standard header/framework search paths.
-  '-F %%clang-importer-sdk-path/frameworks '
-  '-I %%clang-include-dir '
-  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
-
 ###
 
 def disallow(execName):
@@ -984,6 +950,7 @@ config.target_msvc_runtime_opt = ''
 config.target_static_library_prefix = 'lib'
 config.target_static_library_suffix = '.a'
 config.target_env_prefix = ''
+config.target_sdk_libcxx_path = ''
 
 if run_vendor == 'apple':
     target_specific_module_triple = '{}-apple-{}'.format(
@@ -1000,6 +967,7 @@ if run_vendor == 'apple':
         config.target_codesign = "codesign -f -s -"
     config.target_library_path_var = "DYLD_LIBRARY_PATH"
     config.target_runtime = "objc"
+    config.target_sdk_libcxx_path = os.path.join(config.variant_sdk, 'usr', 'include', 'c++', 'v1')
 
     config.available_features.add('libdispatch')
     config.available_features.add('foundation')
@@ -2297,6 +2265,45 @@ if platform.system() != 'Darwin' or swift_test_mode == 'optimize_none_with_impli
 # When changing substitutions, update docs/Testing.md.
 #
 
+if config.target_sdk_libcxx_path != '':
+    config.substitutions.append(('%cxx-stdlib-include', '-nostdinc++ -isystem "%s"' % config.target_sdk_libcxx_path))
+else:
+    config.substitutions.append(('%cxx-stdlib-include', ''))
+
+extraCheckWarningFlags = (
+  # Turn on all warnings and promote them to errors
+  '-Weverything -Werror '
+  # Don't warn about unused macros in our clang header.
+  '-Wno-unused-macros '
+  # Don't warn about module imports used at #includes.
+  '-Wno-incomplete-module -Wno-auto-import '
+  # Don't warn about any variadic macros we might have.
+  '-Wno-variadic-macros '
+  # Don't warn about any C++98 compatibility issues.
+  '-Wno-c++98-compat-pedantic '
+  # Don't warn about poison system directories in the Linux system paths.
+  '-Wno-poison-system-directories '
+  # For -fmodules-cache-path, when modules are off.
+  '-Wno-unused-command-line-argument '
+  # Don't warn about nullability specifiers in C/C++ code.
+  '-Wno-nullability-extension ')
+
+# Verifies that a C++ file can be compiled without warnings except for some exceptions.
+config.substitutions.insert(0, ('%check-c-header-in-clang',
+  '%clang -fsyntax-only -x c-header ' + extraCheckWarningFlags +
+  # Use standard header/framework search paths.
+  '-F %%clang-importer-sdk-path/frameworks '
+  '-I %%clang-include-dir '
+  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
+
+# Verifies that a C++ file can be compiled without warnings except for some exceptions.
+config.substitutions.insert(0, ('%check-cxx-header-in-clang',
+  '%clangxx -fsyntax-only -x c++-header ' + extraCheckWarningFlags +
+  # Use standard header/framework search paths.
+  '-F %%clang-importer-sdk-path/frameworks '
+  '-I %%clang-include-dir %%cxx-stdlib-include '
+  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
+
 # Different OS's require different prefixes for the environment variables to be
 # propagated to the calling contexts.
 # In order to make tests OS-agnostic, names of environment variables should be