add cflags for -mtune to target arch variant

Change-Id: I0b3693ce2f478e52d559d6007d1ae50830aa4d72
Restore LDFLAGS to -O2 and add -Wl,--sort-common -s

O3 is potentially funky, linaro has O2, and THE INTERNET SAYS --sort-common -s is FTW

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

-VanirAOSP

Change-Id: Ic69fe56b0473f233f06f8507bf496d8807e5a0f0