BN_LLONG is only ever used in #ifdefs. The actual type is BN_ULLONG. Switch the
ifdefs to check on BN_ULLONG and remove BN_LLONG. Also fix signedness of all
the constants (potentially avoiding undefined behavior in some operations).
Change-Id: I3e7739bbe14c50ea7db04fc507a034a8cb315a5f
Reviewed-on: https://boringssl-review.googlesource.com/6518
Reviewed-by: Adam Langley <agl@google.com>