move __do_oserror and __inviocb into their own source files

git-svn-id: svn://svn.cc65.org/cc65/trunk@4487 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/atari/do_oserr.s

@@ -0,0 +1,15 @@
+;
+; this routine updates errno.  do a JMP here right after calling
+; CIOV.	 we expect status in Y.
+; __retminus is a routine with returns AX with $FFFF
+;
+	.include "errno.inc"
+
+	.export __do_oserror, __retminus
+
+__do_oserror:
+	sty	__oserror	; save os dependent error code
+__retminus:
+	lda	#$FF
+	tax			; return -1
+	rts