Enhance RGBASM warning diagnostics: #2968

Job	Run time
macos-static	2m 24s
windows-mingw-build (32)	56s
windows (32, windows-2019)	4m 44s
windows-mingw-build (64)	1m 41s
unix (ubuntu-20.04, g++, make)	5m 20s
windows (32, windows-2022)	5m 23s
unix (ubuntu-20.04, g++, cmake)	5m 21s
windows (64, windows-2019)	5m 39s
unix (ubuntu-20.04, clang++, make)	5m 50s
windows (64, windows-2022)	4m 1s
unix (ubuntu-20.04, clang++, cmake)	5m 49s
unix (ubuntu-22.04, g++, make)	5m 34s
unix (ubuntu-22.04, g++, cmake)	5m 44s
unix (ubuntu-22.04, clang++, make)	4m 9s
unix (ubuntu-22.04, clang++, cmake)	4m 9s
unix (macos-14, clang++, make)	5m 32s
unix (macos-14, clang++, cmake)	6m 0s
windows-mingw-testing (windows-2019, 32)	4m 38s
windows-mingw-testing (windows-2019, 64)	4m 13s
windows-mingw-testing (windows-2022, 32)	3m 53s
windows-mingw-testing (windows-2022, 64)	4m 29s
	1h 35m 29s

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