COMPILE_ONLY in bcm_test should use object library

See this comment from @eldiener:

> Why not have the line:
> 
> add_library(${PARSE_NAME} STATIC EXCLUDE_FROM_ALL ${SOURCES})
> 
> be instead:
> 
> add_library(${PARSE_NAME} OBJECT EXCLUDE_FROM_ALL ${SOURCES})
> 
> if it works. This would allow just the creation of object files rather than the creation of a static library, which is overkill in this situation.