AIX: Implement shared_target = "aix-solib" support

AIX: Implement shared_target = "aix-solib" support

This builds shared libraries as libxxx.so, libxxx.so.ver and static
libraries as libxxx.a.  For shlib_variant builds, it builds libxxx.so,
libxxxvariant.so.ver, and libxxxx.a.  libxxx.so is a linker import
library that directs the linker to embed a run-time dependency
reference to libxxxvariant.so.ver.  Only libxxxvariant.so.ver is needed
at runtime.

Fixes #21518

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21540)