[PATCH] [5.12] Allow build on aix 4.2 (sigaction and IPv6)

[PATCH] [5.12] Allow build on aix 4.2 (sigaction and IPv6)

Based on a patch by AUGUSTE-ETIENNE José <jose.auguste-etienne@cgss-guyane.fr>

The attached patches are necessary to work around aix 4.2 lack of support for IPv6,
and limited support for POSIX sigaction()

The hints/aix_4.sh patch solves the following build failure:

"Socket.xs", line 468.16: 1506-007 (S) "struct in6_addr" is undefined.

The ext/POSIX/t/sigaction.t patch solves the failing test reported a looong time ago:

http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-01/msg01124.html

After testing a simple C program using POSIX sigaction() with SA_SIGINFO,
I found that it worked on aix 4.3 but failed on aix 4.2.

I think it's safe to skip the SA_SIGINFO test on the aix 4.2 platform.

perl 5.12.0 builds fine on the following platforms / C compiler :

aix 4.2.1 / vac 5.0.2.7 (with attached patches)
aix 4.3.2 / gcc 2.95.3
aix 4.3.3 / vac 4.4.0.3
aix 4.3.3 / vac 5.0.28
aix 5.2 / GNUpro gcc 2.9.aix51.020209

The atatched patches should be applied to blead and maint.