[OpenMP][OMPD] Fix GDB plugin to work correctly when installed (#153956)

Fix the `sys.path` logic in the GDB plugin to insert the intended
self-path in the first position rather than appending it to the end. The
latter implied that if `sys.path` (naturally) contained the GDB's
`gdb-plugin` directory, `import ompd` would return the top-level
`ompd/__init__.py` module rather than the `ompd/ompd.py` submodule, as
intended by adding the `ompd/` directory to `sys.path`.

This is intended to be a minimal change necessary to fix the issue.
Alternatively, the code could be modified to import `ompd.ompd` and stop
modifying `sys.path` entirely. However, I do not know why this option
was chosen in the first place, so I can't tell if this won't break
something.

Fixes #153954

Signed-off-by: Michał Górny <[email protected]>

Author: mgorny

openmp/libompd/gdb-plugin/ompd/__init__.py

@@ -4,7 +4,7 @@
 
 if __name__ == "__main__":
     try:
-        sys.path.append(os.path.dirname(__file__))
+        sys.path.insert(0, os.path.dirname(__file__))
 
         import ompd