PSX build flags
Re-tighten default compiler options.

Remove "-Wno-unused-parameter -Wno-unused-but-set-parameter" added for
GCC 4.8 experiment.

BUG: 10495043
(cherry picked from internal master 1cea0755f400c1d183d22679d5b931c3a04ae4a4)

Change-Id: Ifa221709b1351a9268c06872e2b667138995c3da

Conflicts:
	core/combo/TARGET_linux-arm.mk
Make cpu-specific optimizations simpler, smarter, and more compatible with CM

infer what we use TARGET_ARCH_VARIANT_CPU for form TARGET_CPU_VARIANT
if TARGET_ARCH_VARIANT_CPU is undefined (as is the case with a virgin CM
device tree.
(based on 720710b - build: Cleanup CPU-specific optimizations (4 weeks ago) <Steve Kondik>)

assume some things are always true, and remove vestigial variables

Change-Id: I7e5c5809b1dc3f19e99cb153461876077b237345

Conflicts:
	core/combo/arch/arm/armv7-a-neon.mk
	core/combo/arch/arm/armv7-a.mk

Conflicts:
	core/combo/arch/arm/armv7-a-neon.mk