Use Thumb2 consistently on armv7-apple-ios and armv7s-apple-ios

[briansmith]

From some PerlAsm, this is apparently the way to do this:

#if __ARM_MAX_ARCH__>=7
.arch	armv7-a
.fpu	neon

.text
.syntax	unified 	@ ARMv7-capable assembler is expected to handle this
#if defined(__thumb2__) && !defined(__APPLE__)
.thumb
#else
.code   32
# undef __thumb2__
#endif

That may be for an older version of the iOS toolchain; newer versions of the iOS toolchain might understand .thumb the same way as other toolchains.

[briansmith]

In particular, x25519-asm-arm.S isn't using Thumb-2 yet.

[briansmith]

Closing this because 32-bit iOS isn't a thing anymore.