Clang 16 will not allow implicit int function defitions by default.
This patch gives all functions a proper definitons.

See also: https://wiki.gentoo.org/wiki/Modern_C_porting

Bug: https://bugs.gentoo.org/878611
Upstream PR: https://github.com/jduerstock/zoo/pull/1

--- a/fiz.c
+++ b/fiz.c
@@ -24,6 +24,7 @@ file by supplying the offset of the file.
 void prtctrl ();
 void prtch ();
 
+int
 main(argc,argv)
 register int argc;
 register char **argv;
--- a/mstime.i
+++ b/mstime.i
@@ -12,6 +12,7 @@ static char mstimeid[]="@(#) mstime.i 2.2 88/01/24 12:47:58";
 Function mstime() converts time in seconds since January 1 of BASEYEAR
 to MS-DOS format date and time.
 */
+void
 mstime(longtime, date, time)
 long longtime;       /* input:  seconds since Jan 1, BASEYEAR   */
 int *date, *time;    /* output: MS-DOS format date and time */
--- a/zoo.c
+++ b/zoo.c
@@ -44,6 +44,7 @@ int next_arg = FIRST_ARG; /* filenames start at this position */
 int arg_count;          /* count of arguments supplied to program */
 char **arg_vector;      /* vector of arguments supplied to program */
 
+int
 main(argc,argv)
 register int argc;
 register char **argv;
--- a/zoofilt.c
+++ b/zoofilt.c
@@ -41,8 +41,10 @@ char *option;
 	unsigned int filetag;							/* tag stored in input */
 	int stat1, stat2, stat3;						/* status codes */
 	int use_lzh = 0;									/* use lzh instead */
-	extern lzc(), lzh_encode();					/* possible encoders */
-	extern lzd(), lzh_decode();					/* and decoders */
+	extern int lzc();					/* possible encoders */
+	extern int lzh_encode();
+	extern int lzd();					/* and decoders */
+	extern int lzh_decode();
 
 	while (*++option) {
 		switch (*option) {
--- a/nixtime.i
+++ b/nixtime.i
@@ -20,7 +20,7 @@
 Function gettime() gets the date and time of the file handle supplied.
 Date and time is in MSDOS format.
 */
-int gettime (file, date, time)
+void gettime (file, date, time)
 ZOOFILE file;
 unsigned *date, *time;
 {
--- a/zoofns.h
+++ b/zoofns.h
@@ -46,7 +46,7 @@
 int exists PARMS ((char *));
 int getfile PARMS ((ZOOFILE, ZOOFILE, long, int));
 int getutime PARMS ((char *, unsigned *, unsigned *));
-int gettime PARMS ((ZOOFILE, unsigned *, unsigned *));
+void gettime PARMS ((ZOOFILE, unsigned *, unsigned *));
 T_SIGNAL handle_break PARMS ((int));
 
 #ifdef USE_ASCII