add a `@trap` builtin

[andrewrk]

This can be very similar to @breakpoint.

zig/lib/std/os.zig

Lines 552 to 558 in 4789cc0

	if (builtin.os.tag == .wasi) {
	exit(1);
	}
	if (builtin.os.tag == .cuda) {
	// TODO: introduce `@trap` instead of abusing https://github.com/ziglang/zig/issues/2291
	@"llvm.trap"();
	}

It should be used in the os.abort implementation for WASI because it causes runtimes to generate a nice stacktrace instead of just exiting.

If a trap is not representable in any particular target, then it can be a compile error. Most targets will have a way to lower trap, however.

This is a contributor-friendly issue for anyone wishing to gently touch many different phases of the compiler pipeline.