tools: mark local C functions as static (#120)

tools/blkpack.c

@@ -6,7 +6,7 @@
 #include <string.h>
 #include <sys/stat.h>
 
-void usage()
+static void usage()
 {
     fprintf(stderr, "Usage: blkpack dirname\n");
 }

tools/common.c

@@ -16,7 +16,7 @@ void mread(int fd, char *s, int count)
     }
 }
 
-void mexpect(int fd, char ec)
+static void mexpect(int fd, char ec)
 {
     char c;
     mread(fd, &c, 1);