More CFLAGS fixes.
More CFLAGS fixes.

Removing CFLAGS setting in the kernel exposed problems in the ones
generated in Makefile.flags, on some platforms.

seL4/common-tool,seL4/common-tool,hendersa/px4-common-tool,winksaville/common-tool,winksaville/common-tool,hendersa/px4-common-tool,hendersa/px4-common-tool,winksaville/common-tool,seL4/common-tool