Update NSPR to 4.12 and NSS to 3.23 on iOS

nss/lib/libpkix/pkix_pl_nss/system/pkix_pl_lifecycle.c

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /*
  * pkix_pl_lifecycle.c
  *
  * Lifecycle Functions for the PKIX PL library.
  *
  */
 
@@ skipping 117 matching lines @@
          */
         if (pkix_pl_initialized) {
             PKIX_RETURN(OBJECT);
         }
 
         classTableLock = PR_NewLock();
         if (classTableLock == NULL) {
             return PKIX_ALLOC_ERROR();
         }
 
-        if (PR_GetEnv("NSS_STRICT_SHUTDOWN")) {
+        if (PR_GetEnvSecure("NSS_STRICT_SHUTDOWN")) {
             pkixLog = PR_NewLogModule("pkix");
         }
         /*
          * Register Object, it is the base object of all other objects.
          */
         pkix_pl_Object_RegisterSelf(plContext);
 
         /*
          * Register Error and String, since they will be needed if
          * there is a problem in registering any other type.
@@ skipping 106 matching lines @@
             /* The library was not initilized */
             PKIX_RETURN(OBJECT);
         }
 
         PR_DestroyLock(classTableLock);
 
         pkix_pl_HttpCertStore_Shutdown(plContext);
 
 #ifdef DEBUG
         numLeakedObjects = pkix_pl_lifecycle_ObjectLeakCheck(NULL);
-        if (PR_GetEnv("NSS_STRICT_SHUTDOWN")) {
+        if (PR_GetEnvSecure("NSS_STRICT_SHUTDOWN")) {
            PORT_Assert(numLeakedObjects == 0);
         }
 #else
         pkix_pl_lifecycle_ObjectLeakCheck(NULL);
 #endif
 
         if (plContext != NULL) {
                 PKIX_PL_NssContext_Destroy(plContext);
         }
 
         pkix_pl_initialized = PKIX_FALSE;
 
         PKIX_RETURN(OBJECT);
 }