instead of embedding the compiler in the check-cases process, spawn the compiler as a sub-process and communicate the updates using the compiler protocol

[andrewrk]

Extracted from #14647.

zig/test/src/Cases.zig

Lines 989 to 991 in b4d58e9

	// TODO: instead of embedding the compiler in this process, spawn the compiler
	// as a sub-process and communicate the updates using the compiler protocol.
	pub fn main() !void {

zig/test/src/Cases.zig

Lines 455 to 472 in b4d58e9

	incremental_exe: *std.Build.CompileStep,
	) void {
	for (self.incremental_cases.items) |incr_case| {
	if (opt_test_filter) |test_filter| {
	if (std.mem.indexOf(u8, incr_case.base_path, test_filter) == null) continue;
	}
	const case_base_path_with_dir = std.fs.path.join(b.allocator, &.{
	cases_dir_path, incr_case.base_path,
	}) catch @panic("OOM");
	const run = b.addRunArtifact(incremental_exe);
	run.setName(incr_case.base_path);
	run.addArgs(&.{
	case_base_path_with_dir,
	b.zig_exe,
	});
	run.expectStdOutEqual("");
	parent_step.dependOn(&run.step);
	}

zig/build.zig

Lines 69 to 73 in b4d58e9

	const check_case_exe = b.addExecutable(.{
	.name = "check-case",
	.root_source_file = .{ .path = "test/src/Cases.zig" },
	.optimize = optimize,
	});