Include <string.h> for the strcmp function.  Increases compatibility
with future compilers which are likely to reject implicit function
declarations by default.

diff --git a/sha2prog.c b/sha2prog.c
index 012701e89898dbda..4c633a68b89501c1 100644
--- a/sha2prog.c
+++ b/sha2prog.c
@@ -33,6 +33,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sysexits.h>
 #include <sys/types.h>
 #include <sys/uio.h>