clipboard: tidy up bmp file header assembly #408

Job	Run time
code formatting check	31s
cppcheck	19m 48s
min features with gcc	2m 29s
min features with g++	2m 21s
min features with clang	2m 49s
max features with gcc	3m 49s
max features with g++	2m 52s
max features with clang	4m 37s
max features with clang and AddressSanitized	3m 9s
max features with gcc and DEBUG	3m 5s
max features with gcc for 32-bit arch (legacy OS)	1m 41s
max features with g++ for 32-bit arch (legacy OS)	1m 34s
max features with clang for 32-bit arch (legacy OS)	2m 9s
	50m 54s

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