Add dladdr() for AIX

Although it deviates from the actual prototype of DSO_dsobyaddr(), this
is now ISO C compliant and gcc -Wpedantic accepts the code.

Added DATA segment checking to catch ptrgl virtual addresses. Avoid
memleaks with every AIX/dladdr() call. Removed debug-fprintf()s.
Added test case for DSO_dsobyaddr(), which will eventually call dladdr().
Removed unecessary AIX ifdefs again.

The implementation can only lookup function symbols, no data symbols.
Added PIC-flag to aix*-cc build targets.

As AIX is missing a dladdr() implementation it is currently uncertain our
exit()-handlers can still be called when the application exits. After
dlclose() the whole library might have been unloaded already.

Signed-off-by: Matthias Kraft <makr@gmx.eu>

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5668)