Monster _r patch: try to scan for all known _r variants,

Monster _r patch: try to scan for all known _r variants,
and then use them (under ithreads).  May fail in HP-UX,
and the op/groups is known to be fickle everywhere.  Known
to work in Solaris, Linux, Tru64, IRIX, AIX.  (Some compiler
warnings in AIX since the first arguments of getnetbyaddr
and getnetbyadd_r are of different types.  Thanks, IBM.)

In non-Configure platforms deny the existence of any
of the _r thingies.  (Also add the recently introduced
d_tm_* to places it wasn't already in.)

TODO: the suggested glibc buffer growth retry loop in case
some entries (at least for: gr*, host*) are big.
Forgot win32/config.win64.

p4raw-id: //depot/perl@15238