I set the CFLAGS in CMake by CMAKE_C_FLAGS. Is something like this to set LDFLAGS?
For linking against libraries see Andre's answer.
For linker flags - the following 4 CMake variables:
CMAKE_EXE_LINKER_FLAGS
CMAKE_MODULE_LINKER_FLAGS
CMAKE_SHARED_LINKER_FLAGS
CMAKE_STATIC_LINKER_FLAGS
can be easily manipulated for different configs (debug, release...) with the ucm_add_linker_flags macro of ucm