mkdef: bsd-gcc uses solaris symbol version scripts

As for linux, make bsd-gcc an alias to the solaris semantics for
shared library symbol version handling.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7376)

util/mkdef.pl

@@ -108,6 +108,7 @@ my %OS_data = (
                      platforms  => { UNIX                       => 1,
                                      EXPORT_VAR_AS_FUNCTION     => 0 } },
     linux       => 'solaris',   # alias
+    "bsd-gcc"   => 'solaris',   # alias
     aix         => { writer     => \&writer_aix,
                      sort       => sorter_unix(),
                      platforms  => { UNIX                       => 1,