Eliminate some new warnings found in build testing

arch/arm/src/imxrt/imxrt_start.c

@@ -55,6 +55,7 @@
 #include "imxrt_clockconfig.h"
 #include "imxrt_mpuinit.h"
 #include "imxrt_userspace.h"
+#include "imxrt_serial.h"
 #include "imxrt_start.h"
 #include "imxrt_gpio.h"
 

boards/arm/s32k1xx/s32k118evb/README.txt

@@ -108,3 +108,6 @@ Configurations
       Configures the NuttShell (nsh) located at apps/examples/nsh.  Support
       for builtin applications is enabled, but in the base configuration no
       builtin applications are selected.
+
+      NOTE:  This is a very minimal NSH configuration in order to recude
+      memory usage.  Most of the NSH niceties are not available.

boards/arm/s32k1xx/s32k146evb/README.txt

@@ -100,7 +100,7 @@ Configurations
        115,200 8N1.  This corresponds to the OpenSDA VCOM port.
 
   Configuration Sub-directories
-  -------------------------
+  -----------------------------
 
     nsh:
     ---

wireless/ieee802154/mac802154_assoc.c

@@ -457,7 +457,6 @@ void mac802154_txdone_assocreq(FAR struct ieee802154_privmac_s *priv,
                                FAR struct ieee802154_txdesc_s *txdesc)
 {
   enum ieee802154_status_e status;
-  FAR struct ieee802154_txdesc_s *respdesc;
   FAR struct ieee802154_primitive_s *primitive =
     (FAR struct ieee802154_primitive_s *)txdesc->conf;