Provide access to rm_cs and rm_ds from protected-mode code.

src/arch/i386/include/librm.h

 /* Variables in librm.S, present in the normal data segment */
 extern uint16_t rm_sp;
 extern uint16_t rm_ss;
-extern uint16_t rm_cs;
 extern uint32_t pm_esp;
+extern uint16_t __data16 ( rm_cs );
+#define rm_cs __use_data16 ( rm_cs )
+extern uint16_t __text16 ( rm_ds );
+#define rm_ds __use_text16 ( rm_ds )
 
 /* Functions that librm expects to be able to link to.  Included here
  * so that the compiler will catch prototype mismatches.

src/arch/i386/transitions/librm.S

 	.section ".data16"
 p2r_jump_vector:
 	.word	p2r_jump_target
+	.globl rm_cs
 rm_cs:	.word 0
+	.globl rm_ds
 	.section ".text16.data"
 rm_ds:	.word 0