wasm incremental compilation does not handle object updates

[andrewrk]

Zig version: 0.14.0-dev.2790+d4fe4698d

The wasm linker backend does not have a way to repeat the "prelink" phase. You can reproduce this by having a C object in the compilation and editing it during an incremental update:

build.zig:

const std = @import("std");

pub fn build(b: *std.Build) void {
    const exe = b.addExecutable(.{
        .name = "abc",
        .root_module = b.createModule(.{
            .target = b.resolveTargetQuery(.{
                .cpu_arch = .wasm32,
                .os_tag = .wasi,
            }),
            .optimize = .Debug,
        }),
        .use_llvm = false,
        .use_lld = false,
    });
    exe.addCSourceFiles(.{ .files = &.{"simple.c"} });
    exe.entry = .disabled;

    b.installArtifact(exe);
}

simple.c

int add(int a, int b) {
    return a + b;
}

andy@bark ~/t/abc [1]> zig build -fincremental --watch 
Build Summary: 3/3 steps succeeded
install success
└─ install abc success
   └─ zig build-exe abc Debug wasm32-wasi success 1s

<edit simple.c and save it>

install
└─ install abc
   └─ zig build-exe abc Debug wasm32-wasi 1 errors
error: symbol collision: add
    note: /home/andy/tmp/abc/.zig-cache/o/fd5f01759518ddb8e2561cbdbac2bbaf/simple.o: exported as (i32, i32) -> i32 here
    note: /home/andy/tmp/abc/.zig-cache/o/fd5f01759518ddb8e2561cbdbac2bbaf/simple.o: exported as (i32, i32) -> i32 here
error: 1 compilation errors
Build Summary: 0/3 steps succeeded; 1 failed
install transitive failure
└─ install abc transitive failure
   └─ zig build-exe abc Debug wasm32-wasi 1 errors

The update fails because the wasm linker has no way to repeat the prelink phase. It needs to redo all object parsing and then reconnect any references from Zcu to the newly parsed object data.