start: make stack size strategy configurable

[Aransentin]

With this PR, one can specify what Linux stack-resizing behaviour by setting the appropriate option in std_options. There are three possibilities:

• none, which relies on the default Linux stack size of 8 MiB.
• program_header, which will look through the ELF headers set the stack size using setrlimit. This is the current and default behaviour.
• fixed, which sets the value to a configurable fixed size, compile-time asserted to be divisible by the page size as the syscall wants.

If you don't set any of these values the default of program_header is chosen, which is the current behaviour, so this PR should have no effect on existing code.

This makes makes it possible to remove unnecessary cruft if one e.g. lacks the CAP_SYS_RESOURCE capability (as that is required for increasing values with setrlimit), or when you don't mind the default 8MiB (Those extra setrlimits totally cramp our style when doing "Hey, look what I can do in X bytes and Y syscalls!" demos).

The ".fixed" option means one could also implement a "manual" version of #1639 by using runtime analysis tools. This entire thing should still be revisited when/if that is handled, but I perhaps this PR is an improvement to the status quo.

(this is a fix of a previous PR, #17830, which I think failed the CI due to allowing stack size shrinking.)

[rootbeer]

Looks reasonable to me (an unofficial reviewer).

Would be great if there was some way to at least exercise the different strategies in Zig's tests.... You might be able to follow some of the examples in test/standalone/?

[Aransentin]

Would be great if there was some way to at least exercise the different strategies in Zig's tests.... You might be able to follow some of the examples in test/standalone/?

I suppose I could – but failing to set the stack size is intentionally a silent failure, which means the tests won't actually report any errors in any case. I did verify (with strace) that the different strategies do what they are supposed to do, at least.