[llvm] Give a warning when no dwo files are provided (PR #94336)

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

The test itself:
#include <stdio.h>
#int main() {
#    printf("hello\n");
#    return 0;
#}

Can you change it not to rely on stdio.h. Just returning 0 should be enough to repro correct?

https://github.com/llvm/llvm-project/pull/94336