build/make/Android.mk: set/use qexec appropriately
build/make/Android.mk: set/use qexec appropriately

commands are echo'd when V=1; libs.mk depends on this variable as well

Change-Id: I88f91b9260f16686cfccdf6bd3f29d246521b62e

ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,webmproject/libvpx,mwgoldsmith/vpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx