Support keep-arc flag.

gdb/.Sanitize

@@ -15,6 +15,20 @@
 
 Do-first:
 
+arc_files="arc-tdep.c remote-arc.c"
+
+if ( echo $* | grep keep\-arc > /dev/null ) ; then
+	keep_these_too="${arc_files} ${keep_these_too}"
+	if [ -n "${verbose}" ] ; then
+		echo Keeping ${arc_files}
+	fi
+else
+	lose_these_too="${arc_files} ${lose_these_too}"
+	if [ -n "${verbose}" ] ; then
+		echo Deleting ${arc_files}
+	fi
+fi
+
 # mswin gdb is not really gdbtk, but is close enough for now.
 
 gdbtk_files="gdbtk.c gdbtk.tcl mswin"
@@ -338,8 +352,6 @@ remote-sa.sparc.c
 ser-go32-para.c
 state.c
 state.h
-arc-tdep.c
-remote-arc.c
 
 Do-last: