overhaul tmpfile, tmpnam, and tempnam functions

these all now use the shared __randname function internally, rather
than duplicating logic for producing a random name. incorrect usage of
the access syscall (which works with real uid/gid, not effective) has
been removed, along with unnecessary heavy dependencies like snprintf.

src/stdio/tmpfile.c

@@ -1,19 +1,19 @@
 #include <stdio.h>
 #include <fcntl.h>
-#include <unistd.h>
 #include "stdio_impl.h"
 
 #define MAXTRIES 100
 
+char *__randname(char *);
+
 FILE *tmpfile(void)
 {
-	char buf[L_tmpnam], *s;
+	char s[] = "/tmp/tmpfile_XXXXXX";
 	int fd;
 	FILE *f;
 	int try;
 	for (try=0; try<MAXTRIES; try++) {
-		s = tmpnam(buf);
-		if (!s) return 0;
+		__randname(s+13);
 		fd = sys_open(s, O_RDWR|O_CREAT|O_EXCL, 0600);
 		if (fd >= 0) {
 			f = __fdopen(fd, "w+");