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)