Do not use separate segments for __-prefixed versions of functions.

The __-prefixed versions were introduced for use in <stdio.h> macros that have since been removed, so they are not really necessary any more. However, they may be used in old object files, so those symbols are still included for now.

stdio.asm

@@ -1860,11 +1860,7 @@ stream   ds    4
 ****************************************************************
 *
 fseek    start
-         jmp   __fseek
-         end
-
-__fseek  start
-
+__fseek  entry
 err      equ   1                        return value
 
          csubroutine (4:stream,4:offset,2:wherefrom),2
@@ -2706,10 +2702,7 @@ lb2      ph4   <buf
 ****************************************************************
 *
 setvbuf  start
-         jmp   __setvbuf
-         end
-
-__setvbuf start
+__setvbuf entry
 err      equ   1                        return code
 
          csubroutine (4:stream,4:buf,2:type,4:size),2