Freedom to use any GCC Version

Does not break current builds as GCC 4.6 is set as the default version
If you want to use a newer version add a flag in the BoardConfig for your
device as follow

TARGET_GCC_VERSION := <version-to-use>
eg
TARGET_GCC_VERSION := 4.7

and

TARGET_USE_O3 := <value>
eg
TARGET_USE_O3 := true

Change-Id: Iae44849e28add59bc1810b029fa575bff9c24e50