Backwards compatibility fixes

- Older pythons don't know EXT_SUFFIX
- Linux 4.17-4.19 know PR_GET_SPECULATION_CTRL but not
  PR_SPEC_INDIRECT_BRANCH

_prctlmodule.c

@@ -177,7 +177,11 @@ prctl_prctl(PyObject *self, PyObject *args)
 #endif
 #ifdef PR_GET_SPECULATION_CTRL
         case(PR_SET_SPECULATION_CTRL):
+#ifdef PR_SPEC_INDIRECT_BRANCH
             if(arg != PR_SPEC_STORE_BYPASS && arg != PR_SPEC_INDIRECT_BRANCH) {
+#else
+            if(arg != PR_SPEC_STORE_BYPASS) {
+#endif
                 PyErr_SetString(PyExc_ValueError, "Invalid speculation control setting");
                 return NULL;
             }
@@ -193,7 +197,11 @@ prctl_prctl(PyObject *self, PyObject *args)
             }
             /* Intentionally not breaking */
         case(PR_GET_SPECULATION_CTRL):
+#ifdef PR_SPEC_INDIRECT_BRANCH
             if(arg != PR_SPEC_STORE_BYPASS && arg != PR_SPEC_INDIRECT_BRANCH) {
+#else
+            if(arg != PR_SPEC_STORE_BYPASS) {
+#endif
                 PyErr_SetString(PyExc_ValueError, "Invalid speculation control setting");
                 return NULL;
             }
@@ -793,7 +801,9 @@ PyInit__prctl(void)
 #ifdef PR_SET_SPECULATION_CTRL
     namedattribute(SPECULATION_CTRL);
     namedconstant(PR_SPEC_STORE_BYPASS);
+#ifdef PR_SPEC_INDIRECT_BRANCH
     namedconstant(PR_SPEC_INDIRECT_BRANCH);
+#endif
     namedconstant(PR_SPEC_PRCTL);
     namedconstant(PR_SPEC_ENABLE);
     namedconstant(PR_SPEC_DISABLE);

test_prctl.py

@@ -15,7 +15,7 @@
 so = '.so'
 try:
     import sysconfig
-    so = sysconfig.get_config_var('EXT_SUFFIX')
+    so = sysconfig.get_config_var('EXT_SUFFIX') or sysconfig.get_config_var('SO')
 except ImportError:
     pass