gh-151422: Don't link libffi into _ctypes_test.so

Minor build fix

Author: hoodmane

configure

@@ -8447,9 +8447,12 @@ PY_STDLIB_MOD([_testmultiphase], [test "$TEST_MODULES" = yes], [test "$ac_cv_fun
 PY_STDLIB_MOD([_testsinglephase], [test "$TEST_MODULES" = yes], [test "$ac_cv_func_dlopen" = yes])
 PY_STDLIB_MOD([xxsubtype], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_xxtestfuzz], [test "$TEST_MODULES" = yes])
+dnl _ctypes_test contains only plain C test helpers and does not use libffi
+dnl itself, so it does not need $LIBFFI_CFLAGS/$LIBFFI_LIBS.  We use the
+dnl have_libffi check so the module is only built alongside a working _ctypes.
 PY_STDLIB_MOD([_ctypes_test],
   [test "$TEST_MODULES" = yes], [test "$have_libffi" = yes -a "$ac_cv_func_dlopen" = yes],
-  [$LIBFFI_CFLAGS], [$LIBFFI_LIBS $LIBM])
+  [], [$LIBM])
 
 dnl Limited API template modules.
 dnl Emscripten does not support shared libraries yet.