video_core/cmake: Properly generate fatal errors on Aftermath

Fix "message(ERROR ..." to "message(FATAL_ERROR ..." to properly stop
cmake when Nsight Aftermath can't be configured.

src/video_core/CMakeLists.txt

@@ -288,10 +288,10 @@ target_link_libraries(video_core PRIVATE sirit)
 
 if (ENABLE_NSIGHT_AFTERMATH)
     if (NOT DEFINED ENV{NSIGHT_AFTERMATH_SDK})
-        message(ERROR "Environment variable NSIGHT_AFTERMATH_SDK has to be provided")
+        message(FATAL_ERROR "Environment variable NSIGHT_AFTERMATH_SDK has to be provided")
     endif()
     if (NOT WIN32)
-        message(ERROR "Nsight Aftermath doesn't support non-Windows platforms")
+        message(FATAL_ERROR "Nsight Aftermath doesn't support non-Windows platforms")
     endif()
     target_compile_definitions(video_core PRIVATE HAS_NSIGHT_AFTERMATH)
     target_include_directories(video_core PRIVATE "$ENV{NSIGHT_AFTERMATH_SDK}/include")