Configurations/10-main.conf: always pass -bsrv4 to AIX linker.

This makes AIX build procedure behave more like e.g. Solaris. Most
notably this makes it possible to pass -Wl,-R,'$(LIBRPATH)' at config
time to embed installation destination as library search path into
openssl binary. This doesn't imply that other applications have to be
linked with -bsvr4, they are free to choose whatever appropriate for
given circumstances.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6487)