Prevent changes to COMMON_GLOBAL_C(PP)FLAGS

Reorder the definitions of the core cflags so that we can prevent device
configurations from changing the global C(PP)FLAGS.

There is no reason for devices to be configuring the global cflags -- if
something needs to change for a particular device, that flag should be
defined in the BoardConfig.mk, then used in the individual makefiles
where it is needed. The common global flags also affected host tools,
which should not change between device configurations.

Bug: 26165350
Change-Id: Icece4505ce3d2a9168087d802953378534018d47