bpo-38960: DTrace build fix for FreeBSD. (GH-17451)

DTrace build fix for FreeBSD.

- allowing passing an extra flag as it need to define the arch size.
- casting some probe's arguments.

diff --git a/Python/import.c b/Python/import.c
index 045b6d0..2e5f783 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1762,14 +1762,14 @@
     }
 
     if (PyDTrace_IMPORT_FIND_LOAD_START_ENABLED())
-        PyDTrace_IMPORT_FIND_LOAD_START(PyUnicode_AsUTF8(abs_name));
+        PyDTrace_IMPORT_FIND_LOAD_START((char *)PyUnicode_AsUTF8(abs_name));
 
     mod = _PyObject_CallMethodIdObjArgs(interp->importlib,
                                         &PyId__find_and_load, abs_name,
                                         interp->import_func, NULL);
 
     if (PyDTrace_IMPORT_FIND_LOAD_DONE_ENABLED())
-        PyDTrace_IMPORT_FIND_LOAD_DONE(PyUnicode_AsUTF8(abs_name),
+        PyDTrace_IMPORT_FIND_LOAD_DONE((char *)PyUnicode_AsUTF8(abs_name),
                                        mod != NULL);
 
     if (import_time) {