Fix warnings in the RTS

For some reason this causes build failures for me in my 32-bit chroot,

includes/Cmm.h

@@ -407,9 +407,12 @@
 #define BITMAP_BITS(bitmap) ((bitmap) >> BITMAP_BITS_SHIFT)
 
 /* Debugging macros */
-#define LOOKS_LIKE_INFO_PTR(p)				\
-   ((p) != NULL && 					\
-     (TO_W_(%INFO_TYPE(%STD_INFO(p))) != INVALID_OBJECT) &&	\
+#define LOOKS_LIKE_INFO_PTR(p)                                  \
+   ((p) != NULL &&                                              \
+    LOOKS_LIKE_INFO_PTR_NOT_NULL(p))
+
+#define LOOKS_LIKE_INFO_PTR_NOT_NULL(p)                         \
+   ( (TO_W_(%INFO_TYPE(%STD_INFO(p))) != INVALID_OBJECT) &&     \
      (TO_W_(%INFO_TYPE(%STD_INFO(p))) <  N_CLOSURE_TYPES))
 
 #define LOOKS_LIKE_CLOSURE_PTR(p) (LOOKS_LIKE_INFO_PTR(GET_INFO(UNTAG(p))))

includes/Storage.h

@@ -304,7 +304,10 @@ void dirty_MUT_VAR(StgRegTable *reg, StgClosure *p);
    -------------------------------------------------------------------------- */
 
 #define LOOKS_LIKE_INFO_PTR(p) \
-   (p && ((StgInfoTable *)(INFO_PTR_TO_STRUCT(p)))->type != INVALID_OBJECT && \
+   (p && LOOKS_LIKE_INFO_PTR_NOT_NULL(p))
+
+#define LOOKS_LIKE_INFO_PTR_NOT_NULL(p) \
+   (((StgInfoTable *)(INFO_PTR_TO_STRUCT(p)))->type != INVALID_OBJECT && \
     ((StgInfoTable *)(INFO_PTR_TO_STRUCT(p)))->type < N_CLOSURE_TYPES)
 
 #define LOOKS_LIKE_CLOSURE_PTR(p) \

rts/sm/Storage.c

@@ -116,7 +116,8 @@ initStorage( void )
   /* Sanity check to make sure the LOOKS_LIKE_ macros appear to be
    * doing something reasonable.
    */
-  ASSERT(LOOKS_LIKE_INFO_PTR(&stg_BLACKHOLE_info));
+  /* We use the NOT_NULL variant or gcc warns that the test is always true */
+  ASSERT(LOOKS_LIKE_INFO_PTR_NOT_NULL(&stg_BLACKHOLE_info));
   ASSERT(LOOKS_LIKE_CLOSURE_PTR(&stg_dummy_ret_closure));
   ASSERT(!HEAP_ALLOCED(&stg_dummy_ret_closure));