Rename ffz() function to fio_ffz() to avoid conflicts

Newer gcc/glibc include an ffz function. Lets just do the easy
thing and rename ours to fio_ffz(), then we can look into reusing
a provided one later if necessary.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/arch/arch-s390.h b/arch/arch-s390.h
index b7048ad..ed5d462 100644
--- a/arch/arch-s390.h
+++ b/arch/arch-s390.h
@@ -12,7 +12,7 @@
 #define __NR_fadvise64		253
 #endif
 
-#define nop	asm volatile ("diag 0,0,68" : : : "memory")
-#define ffz(v)	generic_ffz((v))
+#define nop		asm volatile ("diag 0,0,68" : : : "memory")
+#define fio_ffz(v)	generic_ffz((v))
 
 #endif