alternative.cmake

macro(_add_static _name)
	add_library(${_name}_uncombined STATIC EXCLUDE_FROM_ALL "${ARGN}")
	# or alternatively
	# add_custom_target(${_name}_uncombined SOURCES "${ARGN}")
	get_target_property(_objs ${_name}_uncombined SOURCES)
	string(REPLACE ";" " " _objs "${_objs}")
	add_custom_command(
		OUTPUT ${_name}_combined.o
		COMMAND
			ld -r ${_objs} -o ${_name}_combined.o
		COMMAND
			objcopy --localize-hidden ${_name}_combined.o
	)
	add_library(${_name} STATIC ${_name}_combined.o)
endmacro()

current.cmake

macro(_add_static _name)
	add_library(${_name} STATIC "${ARGN}")
	file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/sharedhidden)
	add_custom_command(
		TARGET ${_name} POST_BUILD
		COMMAND
			${CMAKE_AR} x $<TARGET_FILE:${_name}>
		COMMAND
			ld -r *.o -o ../_combined_${_name}.o
		COMMAND
			objcopy --localize-hidden ../_combined_${_name}.o
		COMMAND
			rm $<TARGET_FILE:${_name}>
		COMMAND
			${CMAKE_AR} rcs $<TARGET_FILE:${_name}> ../_combined_${_name}.o
		WORKING_DIRECTORY ${PROJECT_BINARY_DIR}/sharedhidden
		COMMENT "Removing hidden symbols")
endmacro()

	_add_static(libui
		$<TARGET_OBJECTS:libui-common>
		$<TARGET_OBJECTS:libui-${_OSDIR}>
	)

common folder:
add_library(libui-common OBJECT files...)
unix folder:
add_library(libui-unix OBJECT files...)