Hello!
This PR fixes#63871. Clang should no longer crash and instead emits an
error message.
Below is an example of the new error message:
```
~/dev/fork-llvm-project omp_dispatch_unimpl
❯ ./install/bin/clang -fopenmp -c -emit-llvm -Xclang -disable-llvm-passes test.c
test.c:6:5: error: cannot compile this OpenMP dispatch directive yet
6 | #pragma omp dispatch
| ^~~~~~~~~~~~~~~~~~~~
1 error generated.
```
