Allow defining multiple GCC O Levels [1/2]

Available GCC Optimization Levels
    -Os
    -O2 (Default)
    -O3

PS2: Derp fix
PS3: Derp fix 2.0

Change-Id: I55fa04026df24841b9d67325242ce3cb460726a1
Signed-off-by: Lokesh Chamane <lokesh.c703@gmail.com>
ccache: Use system version over prebuilt

If there is a ccache binary on the
host system use it instead of the
AOSP prebuilt.

Change-Id: I4b1e030713be22167a12bd229a4e35eda7736cd2
Signed-off-by: Evan Anderson <evan1124@gmail.com>