fix deadlock with build-exe on an object for windows

The steps to repro this issue are:

zig build-obj hello.zig -target x86_64-windows-msvc
zig build-exe hello.obj -target x86_64-windows-msvc --subsystem console
-lkernel32 -lntdll

What was happening is that the main Compilation added a work item to
produce kernel32.lib. Then it added a sub-Compilation to build zig's
libc, which ended up calling a function with extern "kernel32", which
caused the sub-Compilation to also try to produce kernel32.lib. The main
Compilation and sub-Compilation do not coordinate about the set of
import libraries that they will be trying to build, so this caused a
deadlock.

This commit solves the problem by disabling the extern "foo" feature
from working when building compiler_rt or libc. Zig's linker code is now
responsible for putting the appropriate import libs on the linker line,
if any for compiler_rt and libc.

Related: ziglang#5825

Author: andrewrk

src/Compilation.zig

@@ -3174,6 +3174,11 @@ pub fn build_crt_file(
 }
 
 pub fn stage1AddLinkLib(comp: *Compilation, lib_name: []const u8) !void {
+    // Avoid deadlocking on building import libs such as kernel32.lib
+    // This can happen when the user uses `build-exe foo.obj -lkernel32` and then
+    // when we create a sub-Compilation for zig libc, it also tries to build kernel32.lib.
+    if (comp.bin_file.options.is_compiler_rt_or_libc) return;
+
     // This happens when an `extern "foo"` function is referenced by the stage1 backend.
     // If we haven't seen this library yet and we're targeting Windows, we need to queue up
     // a work item to produce the DLL import library for this.

test/standalone.zig

@@ -15,6 +15,7 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/static_c_lib/build.zig");
     cases.addBuildFile("test/standalone/issue_339/build.zig");
     cases.addBuildFile("test/standalone/issue_794/build.zig");
+    cases.addBuildFile("test/standalone/issue_5825/build.zig");
     cases.addBuildFile("test/standalone/pkg_import/build.zig");
     cases.addBuildFile("test/standalone/use_alias/build.zig");
     cases.addBuildFile("test/standalone/brace_expansion/build.zig");

test/standalone/issue_5825/build.zig

@@ -0,0 +1,24 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    const target = .{
+        .cpu_arch = .x86_64,
+        .os_tag = .windows,
+        .abi = .msvc,
+    };
+    const mode = b.standardReleaseOptions();
+    const obj = b.addObject("issue_5825", "main.zig");
+    obj.setTarget(target);
+    obj.setBuildMode(mode);
+
+    const exe = b.addExecutable("issue_5825", null);
+    exe.subsystem = .Console;
+    exe.linkSystemLibrary("kernel32");
+    exe.linkSystemLibrary("ntdll");
+    exe.setTarget(target);
+    exe.setBuildMode(mode);
+    exe.addObject(obj);
+
+    const test_step = b.step("test", "Test the program");
+    test_step.dependOn(&exe.step);
+}

test/standalone/issue_5825/main.zig

@@ -0,0 +1,5 @@
+const std = @import("std");
+
+pub fn main() anyerror!void {
+    std.log.info("All your codebase are belong to us.", .{});
+}