caching of comptime function calls

[andrewrk]

export fn _start() noreturn {
 assert(List(i32) == List(i32));
 exit(0);
}

fn List(T: type) type {
 return struct {
 items: []T,
 capacity: usize,
 };
}

fn assert(ok: bool) {
 if (!ok) @panic("test fail");
}

fn exit(code: usize) noreturn {
 asm volatile ("syscall"
 :
 : [number] "{rax}" (231),
 [arg1] "{rdi}" (code)
 : "rcx", "r11", "memory"
 );
 unreachable;
}

[andrewrk]

Covered by this behavior test:

zig/test/behavior/eval.zig

Lines 161 to 172 in a7c05c0

	test "comptime function with the same args is memoized" {
	comptime {
	try expect(MakeType(i32) == MakeType(i32));
	try expect(MakeType(i32) != MakeType(f64));
	}
	}
	fn MakeType(comptime T: type) type {
	return struct {
	field: T,
	};
	}