improve deprecation warning macro

fix #1488

although, curiously enough, I was never able to reproduce the issue
(according to the bug report, it should be present while using gcc 4.8).

tests/zbufftest.c

@@ -81,7 +81,7 @@ static U64 g_clockTime = 0;
     @return : a 27 bits random value, from a 32-bits `seed`.
     `seed` is also modified */
 #  define FUZ_rotl32(x,r) ((x << r) | (x >> (32 - r)))
-unsigned int FUZ_rand(unsigned int* seedPtr)
+static unsigned int FUZ_rand(unsigned int* seedPtr)
 {
     U32 rand32 = *seedPtr;
     rand32 *= prime1;
@@ -467,7 +467,7 @@ _output_error:
 /*-*******************************************************
 *  Command line
 *********************************************************/
-int FUZ_usage(const char* programName)
+static int FUZ_usage(const char* programName)
 {
     DISPLAY( "Usage :\n");
     DISPLAY( "      %s [args]\n", programName);