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,
	};
	}