cmake: set -Wimplicit-fallthrough=5 for GCC if available
cmake: set -Wimplicit-fallthrough=5 for GCC if available

Change-Id: Ie95ea0e258c81953a663ce375828cb89888ae649
Signed-off-by: Markus Metzger <5f675b2b36595f90898e014b548ff7d9bbff2ab7@intel.com>

01org/processor-trace,01org/processor-trace,01org/processor-trace