fix errno related underscores in all libsrc/*.s files

libsrc/geos-common/system/oserror.s

@@ -3,16 +3,16 @@
 ; GEOS port: Maciej 'YTM/Elysium' Witkowiak
 ; 2.7.2001
 ;
-; int __fastcall__ _osmaperrno (unsigned char oserror);
+; int __fastcall__ __osmaperrno (unsigned char oserror);
 ; /* Map a system specific error into a system independent code */
 ;
 
-            .export __osmaperrno
+            .export ___osmaperrno
 
             .include "errno.inc"
             .include "const.inc"
 
-__osmaperrno:
+___osmaperrno:
         ldx #ErrTabSize
 @L1:    cmp ErrTab-2,x          ; Search for the error code
         beq @L2                 ; Jump if found

libsrc/geos-common/system/setoserror.s

@@ -5,10 +5,10 @@
 ;
 
             .export setoserror
-            .import __oserror
+            .import ___oserror
 
 setoserror:
-        stx __oserror
+        stx ___oserror
         txa
         ldx #0                  ; X is cleared (high byte for promoting char to int)
         tay                     ; Y register is used just to save flags state