Avoid implicit ints, to improve compatibility with future compilers

which may rejected them by default.

diff --git a/null.c b/null.c

index 435025ded8ecb0b7..7ba7ed2bcfbb8715 100644

--- a/null.c

+++ b/null.c

@@ -179,6 +179,7 @@ int f;

 }

 int minmaxfb(f,fb)

+int f,fb;

 {

   int i,j=-1;