[Macros/Tests] Build test plugins with the same compiler as the dylib

Sanitizer ABI are apparently not stable. We need to build the executable
with the same compiler as the linking dylib.

rdar://119141141

test/Macros/lit.local.cfg

@@ -21,11 +21,12 @@ if get_target_os() in ['windows-msvc']:
 else:
     # FIXME(compnerd) do all the targets we currently support use SysV ABI?
     config.substitutions.insert(0, ('%target-abi', 'SYSV'))
+    config.substitutions.insert(0, ('%cmake-c-compiler', config.cmake_c_compiler))
     config.substitutions.insert(
         0,
         (
             '%swift-build-c-plugin',
-            '%clang %c-flags %exe-linker-flags -isysroot %host_sdk -I %swift_src_root/include -L %swift-lib-dir -l_swiftMockPlugin -Xlinker -rpath -Xlinker %swift-lib-dir'
+            '%cmake-c-compiler %c-flags %exe-linker-flags -target %host_triple -isysroot %host_sdk -I %swift_src_root/include -L %swift-lib-dir -l_swiftMockPlugin -Xlinker -rpath -Xlinker %swift-lib-dir'
         )
     )
     config.substitutions.append(('%c-flags', config.c_flags))

test/lit.site.cfg.in

@@ -44,6 +44,8 @@ config.swift_driver_test_options = "@SWIFT_DRIVER_TEST_OPTIONS@"
 config.swift_frontend_test_options = "@SWIFT_FRONTEND_TEST_OPTIONS@"
 config.swift_ide_test_test_options = "@SWIFT_IDE_TEST_TEST_OPTIONS@"
 
+config.cmake_c_compiler = r'''@CMAKE_C_COMPILER@'''
+config.cmake_cxx_compiler = r'''@CMAKE_CXX_COMPILER@'''
 config.c_flags = r'''@CMAKE_C_FLAGS@'''
 config.exe_linker_flags = r'''@CMAKE_EXE_LINKER_FLAGS@'''
 

tools/libMockPlugin/CMakeLists.txt

@@ -16,4 +16,4 @@ add_llvm_symbol_exports(libMockPlugin ${LLVM_EXPORTED_SYMBOL_FILE})
 
 add_dependencies(tools libMockPlugin)
 # Adds -dead_strip option
-add_link_opts(libStaticMirror)
+add_link_opts(libMockPlugin)