Teach clang driver about Cortex-A53 and Cortex-A57.

Adds some Cortex-A53 strings where they were missing before.
Cortex-A57 is entirely new to clang.

Doesn't touch code only used by Darwin, in consequence of which
one of the A53 lines has been removed.

Change-Id: I5edb58f6eae93947334787e26a8772c736de6483
Set appropriate FPU default for Linux on v8

Change-Id: If9b649c92e7196e3e791948545dc80901a0761eb
Clean up char/numeric comparisons in ARM getTargetDefines

Change-Id: Ie07228411b68252adcd5cf80b27ccd2eb3b031d9
Add driver support for FP, SIMD and crypto defaults.

Although we wire up a bit for v8fp for macro setting
purposes, we don't set a macro yet. Need to ask list
about that.

Change-Id: Ic9819593ce00882fbec72757ffccc6f0b18160a0