We were building the NASM flavor with MASM which is why it didn't work. Get the
MASM output working: cpuid and cmove are not available in MASM unless the file
declares .686. Also work around MASM rejecting a very long line in SHA-256.

The follow-up change will get the NASM flavor working. We should probably use
that one as it's documented as supported upstream. But let's make this one
functional too.

Change-Id: Ica69cc042a7250c7bc9ba9325caab597cd4ce616
Reviewed-on: https://boringssl-review.googlesource.com/2091
Reviewed-by: Adam Langley <agl@google.com>

Appease the Chromium build on OS X.

Change-Id: Idb7466b4d3e4cc9161cd09066b2f79a6290838b1
Reviewed-on: https://boringssl-review.googlesource.com/1240
Reviewed-by: Adam Langley <agl@google.com>

(Imported from upstream's ca88a1d439)

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)