CLI: delete redundant logic and use null instead of undef
The `null` value here was missed in
0a4d4eb252a73555a568a532902951a13284d2ef. I hope it is the cause of the
CI failures on Windows.
The fact that libc++ depends on libc is not important for the CLI and
Compilation.create already handles that logic.
469af67804Andrew Kelley committed on 8/3/2023, 4:52:15 PMparentd7e74f7