(Imported from upstream's 64333004a41a9f4aa587b8e5401420fb70d00687.)
RT#4284.
This case should be impossible to hit because |EC_POINT_add| doesn't use
this function and trying to add equal inputs should never occur during a
multiplication. Support for this exists because the pattern has been
copied from the first 64-bit P-224 and P-256 work that Emilia, Bodo and
I did. There it seemed like a reasonable defense-in-depth in case the
code changed in the future.
Change-Id: I7ff138669c5468b7d7a5153429bec728cb67e338
Reviewed-on: https://boringssl-review.googlesource.com/7246
Reviewed-by: David Benjamin <davidben@google.com>
060bd590ce