This is needed to fix all the config APIs to take const char *. I've
split it out as it's the only incompatible half of the change.
Update-Note: External definitions of X509V3_CONF_METHOD will need fix
the types of their functions. There should not be any of these (probably
hide this struct), but if there are, this aligns with upstream OpenSSL.
Change-Id: I6e760cfbca5d3f408215b8f3744acd1fd7f31391
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42727
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>