Make ARM RegNames[] static like X86 (no ARM syms in X86-only build).

Make ARM RegNames[] static like X86 (no ARM syms in X86-only build).

The X86 code was switch out here:
https://codereview.chromium.org/1216933015/diff/150001/src/IceTargetLoweringX86Base.h

The important bit might be that it's static const char * instead of
static IceString. This removes static ctor/dtor for that array,
which LTO doesn't seem to be able to optimize out, leaving ARM
and MIPS symbols in the X86-only build. After changing it to static
const char *, LTO is able to optimize out the ARM and MIPS
symbols in the x86-only build, saving about 3KB of .text and
few bytes of .rodata.

BUG=none
R=jpp@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=0dab032401107239f48cab3605b1f268891cd14e

[jvoung (off chromium), 2015-07-21 17:50:31]

jvoung@chromium.org changed reviewers:
+ jpp@chromium.org, stichnot@chromium.org

[John, 2015-07-21 20:45:29]

lgtm

[jvoung (off chromium), 2015-07-21 21:29:39]

Committed patchset #1 (id:1) manually as
0dab032401107239f48cab3605b1f268891cd14e (presubmit successful).