* src/acconfig.h: Don't protect config.h against multiple

inclusion.
Don't define PARAMS.
* src/system.h: Define PARAMS.
Remove some of the ad-hoc CPP magic for DOS, VMS etc.: this is the
purpose of config.h.  system.h must not try to fix wrong
definitions in config.h.

src/system.h

@@ -34,18 +34,14 @@
 # define getpid _getpid
 #endif
 
-#if defined(HAVE_STDLIB_H) || defined(MSDOS)
+#if HAVE_STDLIB_H
 # include <stdlib.h>
 #endif
 
-#if defined(HAVE_UNISTD_H)
+#if HAVE_UNISTD_H
 # include <unistd.h>
 #endif
 
-#if (defined(VMS) || defined(MSDOS)) && !defined(HAVE_STRING_H)
-# define HAVE_STRING_H 1
-#endif
-
 #if defined(STDC_HEADERS) || defined(HAVE_STRING_H)
 # include <string.h>
 /* An ANSI string.h and pre-ANSI memory.h might conflict.  */
@@ -69,6 +65,11 @@
 extern int errno;
 #endif
 
+#if PROTOTYPES
+# define PARAMS(p) p
+#else
+# define PARAMS(p) ()
+#endif
 
 /*-----------------.
 | GCC extensions.  |