WaitForDebugger function was undefined.

Change-Id: I578e99638bddc40c56817cfc66ed5787f1cdc6e7
Reviewed-on: https://swiftshader-review.googlesource.com/8953Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>