Windows doesn't like struct literals:
..\decrepit\dsa\dsa_decrepit.c(85) : warning C4204: nonstandard extension used : non-constant aggregate initializer

Change-Id: I12541f2883ecbb10c85cddfae8d2adbbb1365ae3
Reviewed-on: https://boringssl-review.googlesource.com/7364
Reviewed-by: Adam Langley <agl@google.com>

This function was deprecated by OpenSSL in 0.9.8 but code that uses it
still exists. This change adds an implementation of this function to
decreipt/ to support these programs.

Change-Id: Ie99cd00ff8b0ab2675f2b1c821c3d664b9811f16
Reviewed-on: https://boringssl-review.googlesource.com/7360
Reviewed-by: David Benjamin <davidben@google.com>