In one of the happy paths, execve() is used to switch to clang in which
case any cleanup logic that exists for this temporary file will not run
and this temp file will be leaked. Oh well. It's a minor punishment for
using `-x c` which nobody should be doing. Therefore, we make no effort
to clean up. Using `-` for stdin as a source file always leaks a temp
file.

Note that the standard `zig build-exe` CLI does not support stdin as an
input file. This is only for `zig cc` C compiler compatibility.