Webkit: Utilize LTO on development builds

Summary: Seeing ~3.2% sunspider improvement on average from 5 runs on a quad core krait 200 locked at 1.2GHz.

Test Plan: Please share your experiences.

Reviewers: randall.rushing, Mustaavalkosta, michyprima, rlasalle15, Roach, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D198

Conflicts:
	Android.mk