Add some cflags to latest GCC versions

Change-Id: Iff1b236e9988f9295b261fe28e1e75eca79755d6
We can use an external toolchain for kernel compilation now.

Change-Id: I0e4043cd1bb11c0b655e00eddbbf3b0719b8972a
Add compilation flags [1]

Change-Id: Iff4b9507be833bd0ab129cacd1a20765ad105c6b