Fixes this error when building for i686:

error: variable 'test' set but not used

--- a/src/crccombine.c
+++ b/src/crccombine.c
@@ -38,7 +38,7 @@
   madler@alumni.caltech.edu
 */
 
-#define STATIC_ASSERT(VVV) do {int test = 1 / (VVV);test++;} while (0)
+#define STATIC_ASSERT(VVV) do {int test = 1 / (VVV);(void)test;test++;} while (0)
 
 #if !((defined(__i386__) || defined(__X86_64__)))