pcre2test: detect setrlimit instead of hardcoding platform list

[puffnfresh]

Replace the growing platform preprocessor check for -S flag support with AC_CHECK_FUNCS/check_symbol_exists detection of setrlimit. This automatically handles any platform lacking setrlimit (WASI, VMS, etc.) without maintaining a manual list.

Haiku and z/OS are kept as explicit exclusions because they provide setrlimit but don't support RLIMIT_STACK.

[NWilson]

Thank you, there are several of these in pcre2test and pcre2grep which I would love to clear up. Much appreciated! I will have to do a little bit of platform checking testing before I merge, but in principle, this is good.

[NWilson]

Hi @puffnfresh.

Thank you very much for this WASI fix!

I would like to merge it. I have now had the chance to do some testing of my own.

I pushed a small fix to your branch, excluding WIN32 as before. This may not be needed... but I have tried a few versions of MinGW, MSYS2, etc, and I'm nervous a regression is possible. Plus - the #if HAVE_SETRLIMIT block where you do the header include is only present on non-Win32.

Secondly, I seem not to have permissions to push merge commits to your branch, so I can't update this PR with a merge from main.

I would like to add the following to build.zig, however it will conflict unless the merge is done:

            .HAVE_SETRLIMIT = is_unix and !is_mingw,

[NWilson]

Needs merge with main, and build.zig update