Clang-tidy: Don't warn about unrecognized compiler flags

When using GCC, clang-tidy will still use clang under the hood but GCC
flags will still be passed. Therefore we will ignore any warnings about
unrecognized flags as we don't care about this when running clang-tidy.

source/CMakeLists.txt

@@ -15,8 +15,9 @@ if(WITH_CLANG_TIDY AND NOT MSVC)
   endif()
 
   find_package(ClangTidy REQUIRED)
-  set(CMAKE_C_CLANG_TIDY ${CLANG_TIDY_EXECUTABLE})
-  set(CMAKE_CXX_CLANG_TIDY ${CLANG_TIDY_EXECUTABLE})
+  set(CMAKE_C_CLANG_TIDY
+    ${CLANG_TIDY_EXECUTABLE};--extra-arg=-Wno-error=unknown-warning-option)
+  set(CMAKE_CXX_CLANG_TIDY ${CLANG_TIDY_EXECUTABLE};--extra-arg=-Wno-error=unknown-warning-option)
 endif()
 
 add_subdirectory(blender)