[librm] Make rm_sp and rm_ss globals again

src/arch/i386/include/librm.h

 	  ( ( ( void * ) (pointer) ) - ( ( void * ) text16 ) ) )
 
 /* Variables in librm.S, present in the normal data segment */
+extern uint16_t rm_sp;
+extern uint16_t rm_ss;
 extern uint16_t __data16 ( rm_cs );
 #define rm_cs __use_data16 ( rm_cs )
 extern uint16_t __text16 ( rm_ds );

src/arch/i386/transitions/librm.S

  ****************************************************************************
  */
 	.section ".data"
+	.globl rm_sp
 rm_sp:	.word 0
+	.globl rm_ss
 rm_ss:	.word 0
 pm_esp:	.long _estack