add_custom_command(OUTPUT output1 [output2 ...]
COMMAND command1 [ARGS] [args1...]
COMMAND command2 [ARGS] [args2...] ...]
[MAIN_DEPENDENCY depend]
[DEPENDS [depends...]]
[IMPLICIT_DEPENDS <lang1> depend1 ...]
[WORKING_DIRECTORY dir]
[COMMENT comment] [VERBATIM] [APPEND])