cmake: prefer the use of target_link_libraries() over set_target_properties(LINKFLAGS), make sure we don't use "-z defs --as-needed" on Mac OS X.

pkg_check_modules.cmake: On first run FindPkgConfig works properly but on second run it does not check if ${prefix}_FOUND is true, patch by Bjoern Ricks submitted by prahal.

pkg_check_modules.cmake: Update the version to work around http://www.cmake.org/Bug/view.php?id=6117 as spotted by prahal.