I would hope any sensible compiler would recognize the rotation. (If
not, we should at least pull this into crypto/internal.h.) Confirmed
that clang at least produces the exact same instructions for
sha256_block_data_order for release + NO_ASM. This is also mostly moot
as SHA-1 and SHA-256 both have assembly versions on x86 that sidestep
most of this.

For the digests, take it out of md32_common.h since it doesn't use the
macro. md32_common.h isn't sure whether it's a multiply-included header
or not. It should be, but it has an #include guard (doesn't quite do
what you'd want) and will get HOST_c2l, etc., confused if one tries to
include it twice.

Change-Id: I1632801de6473ffd2c6557f3412521ec5d6b305c
Reviewed-on: https://boringssl-review.googlesource.com/6650
Reviewed-by: Adam Langley <agl@google.com>