gyp doesn't allow two files to share the same name to avoid bugs in OS X
libtool, so asn1.c's need to all get a prefix.
Change-Id: I3593597912c49dd02655cae329fb253ed4f6f56d
Reviewed-on: https://boringssl-review.googlesource.com/5431
Reviewed-by: Adam Langley <agl@google.com>
