debug: stack capturing now fails in x32 abi executables

[jacobly0]

const std = @import("std");
pub fn main() void {
    var addrs: [0]usize = undefined;
    _ = std.debug.captureCurrentStackTrace(.{}, &addrs);
}

$ zig run repro.zig -target x86_64-linux-muslx32 -lc
thread 732695 panic: attempt to unwrap error: IncompatibleRegisterSize
error return context:
lib/std/debug/Dwarf/SelfUnwinder.zig:315:38: 0x4fb50 in regNative (repro)
    if (bytes.len != @sizeOf(usize)) return error.IncompatibleRegisterSize;
                                     ^

stack trace:
aborting due to recursive panic
Aborted                    (core dumped) zig run repro.zig -target x86_64-linux-muslx32 -lc

[alexrp]

Seems like most uses of usize in std.debug.Dwarf are probably wrong? DWARF should care about register size, not pointer size. So this would presumably break on MIPS N32 too.

Related: #25425

[alexrp]

This will also require some fixes in std.os.linux.x86_64 for x32, e.g. the mcontext_t is just wrong. See: #22189