make: unifdef for other OSes (undefined)

@@ -323,14 +323,12 @@
 extern  long int        hostid;
 
 /*
  * Declarations of system defined variables
  */
-#if !defined(linux)
 /* On linux this variable is defined in 'signal.h' */
 extern  char            *sys_siglist[];
-#endif
 
 /*
  * Declarations of system supplied functions
  */
 extern  int             file_lock(char *, char *, int *, int);

@@ -404,20 +402,18 @@
 #endif
 #if defined(DISTRIBUTED) || defined(MAKETOOL) /* tolik */
 extern  XDR             *get_xdrs_ptr(void);
 #endif
 extern  wchar_t         *getmem_wc(register int size);
-#if !defined(linux)
 /* On linux getwd(char *) is defined in 'unistd.h' */
 #ifdef __cplusplus
 extern "C" {
 #endif
 extern  char            *getwd(char *);
 #ifdef __cplusplus
 }
 #endif
-#endif
 extern  void            handle_interrupt(int);
 extern  Boolean         is_running(Name target);
 extern  void            load_cached_names(void);
 extern  Boolean         parallel_ok(Name target, Boolean line_prop_must_exists);
 extern  void            print_dependencies(register Name target, register Property line);