Allow building with cmake --compile-no-warning-as-error. (#2401)

In CMake 3.24+, there is built-in support for adding -Werror that does
not require adding -Werror explicitly, and allows it to be downgraded to
a warning if the user wants that. Use this, to account for warnings that
have false positives.

test_conformance/extensions/cl_khr_external_semaphore/CMakeLists.txt

@@ -17,6 +17,7 @@ include_directories(${CMAKE_CURRENT_SOURCE_DIR})
 include_directories (${CLConform_INCLUDE_DIR})
 
 list(APPEND CLConform_LIBRARIES vulkan_wrapper)
+set(CMAKE_COMPILE_WARNING_AS_ERROR OFF)
 set(CMAKE_CXX_FLAGS "-fpermissive")
 
 include_directories("../../common/vulkan_wrapper")