Though this doesn't mean that masm becomes supported, the script is
still provided on don't-ask-in-case-of-doubt-use-nasm basis.
See RT#3650 for background.

(Imported from upstream's 2f8d82d641)

The data_word changes were already fixed with our
3e700bb3e812730f60bec529a14c0d35ea9665aa, but best to avoid diverging there.

Change-Id: Iab5455534e8bd632fb2b247ff792d411b105f17a
Reviewed-on: https://boringssl-review.googlesource.com/3581
Reviewed-by: Adam Langley <agl@google.com>