cpp: enable as many warnings as practical

@@ -247,11 +247,11 @@
 char            *skipbl(char *);
 static  char            *unfill(char *);
 static  char            *doincl(char *);
 static  int             equfrm(char *, char *, char *);
 static  char            *dodef(char *);
-static  char            *control(char *);
+void                    control(char *);
 static  struct symtab   *stsym(char *);
 static  struct symtab   *ppsym(char *);
 void            pperror(char *fmt, ...);
 void            yyerror(char *fmt, ...);
 static  void            ppwarn(char *fmt, ...);

@@ -906,11 +906,11 @@
 }
 
 #define fasscan() ptrtab=fastab+COFF
 #define sloscan() ptrtab=slotab+COFF
 
-static char *
+void
 control(p) register char *p; {/* find and handle preprocessor control lines */
         register struct symtab *np;
 for (;;) {
         fasscan(); p=cotoken(p); if (*inp=='\n') ++inp; dump();
         sloscan(); p=skipbl(p);