Cleanup the build by adding missing headers, fixing broken prototypes,
incorrect if statements, and all that jazz

--- arc-5.21m/arc-prototypes.h
+++ arc-5.21m/arc-prototypes.h
@@ -0,0 +1,12 @@
+VOID openarc(int);
+int readhdr(struct heads*, FILE*);
+int match(char*, char*);
+VOID closearc(int);
+int unpack(FILE*, FILE*, struct heads*);
+VOID setstamp(char*, unsigned short, unsigned short);
+int crcbuf(int, u_int, u_char*);
+VOID arcdie();
+int move(char*, char*);
+VOID writehdr(struct heads*, FILE*);
+VOID filecopy(FILE*, FILE*, long);
+VOID upper(char*);
--- arc-5.21m/arc.c
+++ arc-5.21m/arc.c
@@ -105,6 +105,7 @@
 static char   **lst;		/* files list */
 static int	lnum;		/* length of files list */
 
+int
 main(num, arg)			/* system entry point */
 	int		num;	/* number of arguments */
 	char	       *arg[];	/* pointers to arguments */
--- arc-5.21m/arc.h
+++ arc-5.21m/arc.h
@@ -94,6 +94,7 @@
 
 #ifndef DONT_DEFINE		/* Defined by arcdata.c */
 #include "arcs.h"
+#include "arc-prototypes.h"
 
 extern int      keepbak;	/* true if saving the old archive */
 #if	!DOS
--- arc-5.21m/arcext.c
+++ arc-5.21m/arcext.c
@@ -26,8 +26,6 @@
 #include <strings.h>
 #endif
 
-VOID	openarc(), closearc(), setstamp();
-int	match(), readhdr(), unpack();
 static	VOID	extfile();
 
 #ifndef	__STDC__
@@ -144,7 +135,7 @@
 		printf("Extracting file: %s\n", fix);
 
 	if (warn && !overlay) {
-		if (f = fopen(fix, "r")) {	/* see if it exists */
+		if ((f = fopen(fix, "r"))) {	/* see if it exists */
 				fclose(f);
 				printf("WARNING: File %s already exists!", fix);
 				fflush(stdout);
--- arc-5.21m/arclzw.c
+++ arc-5.21m/arclzw.c
@@ -663,7 +663,7 @@
 {
 	int             temp;
 
-	while (temp = string_tab[index].next)	/* while more duplicates */
+	while (temp == string_tab[index].next)	/* while more duplicates */
 		index = temp;
 
 	return index;
--- arc-5.21m/arcmisc.c
+++ arc-5.21m/arcmisc.c
@@ -306,7 +306,7 @@
 
 	if (Nnum == 0) {	/* first call */
 		strcpy(namecopy,filename);
-		if(pattern=rindex(namecopy,CUTOFF)) {
+		if((pattern=rindex(namecopy,CUTOFF))) {
 			*pattern = 0;
 			pattern++;
 			dirname = namecopy;
--- arc-5.21m/arcpack.c
+++ arc-5.21m/arcpack.c
@@ -27,7 +27,6 @@
 
 VOID		setcode(), init_cm(), codebuf();
 VOID		arcdie(), init_sq(), flsh_cm();
-int		crcbuf();
 u_int		ncr_buf();
 
 int		lastc;
--- arc-5.21m/arcrun.c
+++ arc-5.21m/arcrun.c
@@ -20,12 +20,14 @@
  */
 #include <stdio.h>
 #include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 #include "arc.h"
 
 VOID	rempath(), openarc(), closearc(), arcdie();
 int	readhdr(), match(), unpack();
 static	VOID	runfile();
-char	*strcat();
 
 VOID
 runarc(num, arg)		/* run file from archive */
@@ -120,7 +122,7 @@
 #endif
 
 	if (warn)
-		if (tmp = fopen(buf, "r"))
+		if ((tmp = fopen(buf, "r")))
 			arcdie("Temporary file %s already exists", buf);
 	if (!(tmp = fopen(buf, OPEN_W)))
 		arcdie("Unable to create temporary file %s", buf);
@@ -131,7 +133,7 @@
 	dir = gcdir("");	/* see where we are */
 	unpack(arc, tmp, hdr);	/* unpack the entry */
 	fclose(tmp);		/* release the file */
-	chmod(buf, "700");	/* make it executable */
+	chmod(buf, 700);	/* make it executable */
 #if	GEMDOS
 	execve(buf, arg, NULL);
 #else
--- arc-5.21m/arcsvc.c
+++ arc-5.21m/arcsvc.c
@@ -19,15 +19,13 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include "arc.h"
 #if	_MTS
 #include <mts.h>
 #endif
 
-VOID	arcdie(), setstamp();
-int	unlink();
-
 VOID
 openarc(chg)			/* open archive */
 	int             chg;	/* true to open for changes */
--- arc-5.21m/marc.c
+++ arc-5.21m/marc.c
@@ -26,12 +26,14 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #endif
+#include <unistd.h>
 
 #ifndef	__STDC__
 char *calloc(), *malloc(), *realloc(); /* memory managers */
 #endif
-VOID	arcdie();
 static VOID expandlst(), merge();
+int gethdr(FILE*, struct heads*);
+void copyfile(FILE*, struct heads*, int);
 
 FILE *src;			       /* source archive */
 char srcname[STRLEN];		       /* source archive name */
@@ -295,6 +292,7 @@
     else return 0;		       /* or fake end of archive */
 }
 
+void
 copyfile(f,hdr,ver)		       /* copy a file from an archive */
 FILE *f;			       /* archive to copy from */
 struct heads *hdr;		       /* header data for file */