[clang-tidy] openmp-exception-escape check: point to the structured-block

I'm not sure what i was thinking when i wrote it to point at the directive.
It's at the very least confusing, and in the `for` is very misleading.

We should point at the actual Stmt out of which the exception escapes,
to highlight where it should be fixed e.g. via adding try-catch block.

Yes, this breaks existing NOLINT, which is why this change needs to
happen now, not any later.

llvm-svn: 360002