Fix GCC 15.x issues.

--- a/ttcp.c
+++ b/ttcp.c
@@ -157,16 +157,16 @@
 unsigned long numCalls;		/* # of I/O system calls */
 double cput, realt;		/* user, real time (seconds) */
 
-void err();
-void mes();
-void pattern();
+void err(const char *);
+void mes(const char *);
+void pattern(register char *, register int);
 void prep_timer();
-double read_timer();
-int Nread();
-int Nwrite();
-void delay();
-int mread();
-char *outfmt();
+double read_timer(char *, int);
+int Nread(int, void *, int);
+int Nwrite(int, void *, int);
+void delay(int);
+int mread(int, register char *, unsigned int);
+char *outfmt(const double);
 
 int
 main(int argc, char **argv)
@@ -560,7 +560,7 @@
 }
 
 void
-err(char *s)
+err(const char *s)
 {
 	fprintf(stderr, "ttcp%s: ", trans ? "-t" : "-r");
 	perror(s);
@@ -569,7 +569,7 @@
 }
 
 void
-mes(char *s)
+mes(const char *s)
 {
 	fprintf(stderr, "ttcp%s: %s\n", trans ? "-t" : "-r", s);
 }
@@ -586,7 +586,7 @@
 }
 
 char *
-outfmt(double b)
+outfmt(const double b)
 {
     static char obuf[50];
     switch (fmt) {
@@ -616,10 +616,15 @@
 static struct	timeval time0;	/* Time at which timing started */
 static struct	rusage ru0;	/* Resource utilization at the start */
 
-static void prusage();
-static void tvadd();
-static void tvsub();
-static void psecs();
+static void prusage(
+	register struct rusage *,
+	register struct rusage *,
+	struct timeval *,
+	struct timeval *,
+	char *);
+static void tvadd(struct timeval *, struct timeval *, struct timeval *);
+static void tvsub(struct timeval *, struct timeval *, struct timeval *);
+static void psecs(long, register char *);
 
 /*
  *			P R E P _ T I M E R