incremental compilation fails on hello world test case, crash in updateZirRefs

[andrewrk]

Zig Version

0.14.0-dev.438+b5f3d1216

Steps to Reproduce and Observed Behavior

test case (available at test/incremental/hello):

#target=x86_64-linux
#update=initial version
#file=main.zig
const std = @import("std");
pub fn main() !void {
    try std.io.getStdOut().writeAll("good morning\n");
}
#expect_stdout="good morning\n"
#update=change the string
#file=main.zig
const std = @import("std");
pub fn main() !void {
    try std.io.getStdOut().writeAll("おはようございます\n");
}
#expect_stdout="おはようございます\n"

$ stage3/bin/zig run ../tools/incr-check.zig -- stage4/bin/zig ../test/incremental/hello 
error: update 'change the string' failed:
thread 619922 panic: reached unreachable code
/home/andy/dev/zig/lib/std/debug.zig:404:14: 0x18c18ad in assert (zig)
    if (!ok) unreachable; // assertion failure
             ^
/home/andy/dev/zig/src/InternPool.zig:698:27: 0x1f94180 in view (zig)
                    assert(capacity > 0); // optimizes `MultiArrayList.Slice.items`
                          ^
/home/andy/dev/zig/src/Zcu/PerThread.zig:373:37: 0x1d3d9ea in updateZirRefs (zig)
        for (tracked_insts_list.view().items(.@"0"), 0..) |*tracked_inst, tracked_inst_unwrapped_index| {
                                    ^
/home/andy/dev/zig/src/Compilation.zig:3602:33: 0x1b0f249 in performAllTheWorkInner (zig)
            try pt.updateZirRefs();
                                ^
/home/andy/dev/zig/src/Compilation.zig:3496:36: 0x19d2b53 in performAllTheWork (zig)
    try comp.performAllTheWorkInner(main_progress_node);
                                   ^
/home/andy/dev/zig/src/Compilation.zig:2231:31: 0x19cf318 in update (zig)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/andy/dev/zig/src/main.zig:4104:32: 0x1a13cf3 in serve (zig)
                try comp.update(main_progress_node);
                               ^
/home/andy/dev/zig/src/main.zig:3399:22: 0x1a316c6 in buildOutputType (zig)
            try serve(
                     ^
/home/andy/dev/zig/src/main.zig:263:31: 0x18c387a in mainArgs (zig)
        return buildOutputType(gpa, arena, args, .{ .build = .Exe });
                              ^
/home/andy/dev/zig/src/main.zig:209:20: 0x18bf9fa in main (zig)
    return mainArgs(gpa, arena, args);
                   ^
/home/andy/dev/zig/lib/std/start.zig:532:37: 0x18bf0f5 in posixCallMainAndExit (zig)
            const result = root.main() catch |err| {
                                    ^
/home/andy/dev/zig/lib/std/start.zig:277:5: 0x18bec11 in _start (zig)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0xc in ??? (???)
Unwind information for `???:0xc` was not available, trace may be incomplete

Expected Behavior

Passing test case.

[mlugg]

you know shit's getting serious when we have an issue label

[mlugg]

This now hits an ELF linker crash which is tracked by #21165.