Set CPU-specific optimizations for all supported variants

Change-Id: I401fecf5314e854a2a0b3bb2f9b6f6afb3a1b4b4
build: Fix disabling PIE

Commit 419b7227dd7ed2a23faaba0d393d6d6ee5c46925 was not cherry-picked
properly and the correct cflags were never set

Change-Id: I3bc6014fe791e2e8a4cca5106e70f23279c5e43c
build: Set ccache base to build top

This enables ccache sharing between different build tree paths.

Change-Id: I99636bdd2779a6ccf0649f027e35cf67df44b6ae
Don't set CCACHE_BASEDIR if its already set

 * enable use of shared ccache

Change-Id: Ic708a5d5169291d674b167aa2c87bf2c8adaafae
Merge remote-tracking branch 'upstream-omni/android-4.4' into kitkat-mr2