[cmake] configure error with cmake 3.19.1

[JackBoosY]

When using cmake 3.19.1 to configure solid3, it shows:

CMake Error: install(EXPORT "solid3" ...) includes target "solid3" more than once in the export set.
-- Generating done

solid3/src/CMakeLists.txt

Lines 89 to 102 in c53f6bb

	install(
	TARGETS solid3
	EXPORT solid3
	ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT development
	LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT runtime NAMELINK_SKIP
	RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT runtime
	)
	if(DYNAMIC_SOLID)
	install(
	TARGETS solid3
	EXPORT solid3
	LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT development NAMELINK_ONLY
	)
	endif()

It export the target solid3 twice.

Related: microsoft/vcpkg#14716

[rickertm]

The PR in #6 fixes this.

[JackBoosY]

@rickertm I think we should wait for https://discourse.cmake.org/t/error-when-installing-targets-and-exports-in-3-19-1/2245/6 result.