bpo-36763, _testembed: enable assert() in release mode (GH-13857)

(cherry picked from commit 013a18a65167725f140c0395211050ae03501b12)

Co-authored-by: Victor Stinner <vstinner@redhat.com>
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 3e1210e..9633f46 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -1,10 +1,13 @@
-/* FIXME: PEP 587 makes these functions public */
 #ifndef Py_BUILD_CORE_MODULE
 #  define Py_BUILD_CORE_MODULE
 #endif
 
+/* Always enable assertion (even in release mode) */
+#undef NDEBUG
+
 #include <Python.h>
-#include "pycore_initconfig.h"   /* FIXME: PEP 587 makes these functions public */
+#include "pycore_initconfig.h"   /* _PyConfig_InitCompatConfig() */
+#include "pycore_pystate.h"      /* _PyRuntime */
 #include <Python.h>
 #include "pythread.h"
 #include <inttypes.h>