Moved two errno helper functions into separate files.

Only the function that actually is needed will be linked.  It is very useful for targets that do not have file-system I/O.

libsrc/common/errno.s

@@ -1,47 +1,14 @@
 ;
-; Ullrich von Bassewitz, 2003-08-12
+; 2003-08-12, Ullrich von Bassewitz
+; 2015-09-24, Greg King
 ;
-; Helper functions for several high level file functions.
+; extern int _errno;
+; /* Library errors go here. */
 ;
 
-
         .include        "errno.inc"
 
-.code
-
-; ----------------------------------------------------------------------------
-; int __fastcall__ _directerrno (unsigned char code);
-; /* Set errno to a specific error code, clear _oserror and return -1. Used
-; ** by the library.
-; */
-
-__directerrno:
-        jsr     __seterrno              ; Set errno, returns with A = 0
-        sta     __oserror               ; Clear __oserror
-        beq     fail                    ; Branch always
-
-; ----------------------------------------------------------------------------
-; int __fastcall__ _mappederrno (unsigned char code);
-; /* Set _oserror to the given platform specific error code. If it is a real
-; ** error code (not zero) set errno to the corresponding system error code
-; ** and return -1. Otherwise return zero.
-; ** Used by the library.
-; */
-
-__mappederrno:
-        sta     __oserror               ; Store the error code
-        tax                             ; Did we have an error?
-        beq     ok                      ; Branch if no
-        jsr     __osmaperrno            ; Map os error into errno code
-        jsr     __seterrno              ; Save in errno
-fail:   lda     #$FF                    ; Return -1
-        tax
-ok:     rts
-
-
-; ----------------------------------------------------------------------------
 .bss
 
 __errno:
         .word   0
-