build: optionally use the system's ccache

ccache 3.x supports direct mode
(http://ccache.samba.org/manual.html#_the_direct_mode)
This is not supported in the prebuilt version. Direct mode has been
shown to decrease build time by up to 40x, compared to preprocessor mode
used in ccache 2.4, which is substantially less

Thanks to VanirAOSP!
https://github.com/VanirAOSP/build/commit/e802113de5ca54b926c6a7a32b231d10e3a0807a

Change-Id: I6a930eca9244f450c69bc2ca170fc6582f487fc4
LDFLAGS: switch to -O2, -Wl,--sort-common -s

references:
http://forums.gentoo.org/viewtopic.php?t=67777
https://mail.gnome.org/archives/desktop-devel-list/2004-September/msg00377.html
http://www.akkadia.org/drepper/dsohowto.pdf

Thanks to VanirAOSP!
https://github.com/VanirAOSP/build/commit/af4089fe95d3c25b045c9c12fd634e3c6a74c71b

Change-Id: I7e464d51b1b98cb803b0d00ab84f1752892b566a
set ro.secure=0 by default
use host ccache
 proper fix

Change-Id: Ia49187d47979a8eb02ca75b4182504a7c35d6629
Revert "Introduce Link Time Optimization"

This reverts commit 0f92a812c0d128262622e927820ef19ad1646925.