handy.h: Skip non-ptr assertion on old gcc's

See #18655, which this fixes.

handy.h

@@ -1424,9 +1424,16 @@ or casts
 #   define WIDEST_UTYPE U32
 #endif
 
-/* Use this, where there could be some confusion, as a static assert in macros
- * to make sure that a parameter isn't a pointer. */
-#define ASSERT_NOT_PTR(x) ((x) | 0)
+/* Where there could be some confusion, use this as a static assert in macros
+ * to make sure that a parameter isn't a pointer.  But some compilers can't
+ * handle this.  The only one known so far that doesn't is gcc 3.3.6; the check
+ * below isn't thorough for such an old compiler, so may have to be revised if
+ * experience so dictates. */
+#if  ! PERL_IS_GCC || PERL_GCC_VERSION_GT(3,3,6)
+#  define ASSERT_NOT_PTR(x) ((x) | 0)
+#else
+#  define ASSERT_NOT_PTR(x) (x)
+#endif
 
 /* FITS_IN_8_BITS(c) returns true if c doesn't have  a bit set other than in
  * the lower 8.  It is designed to be hopefully bomb-proof, making sure that no
@@ -1443,7 +1450,7 @@ or casts
   /* The '| 0' part ensures a compiler error if c is not integer (like e.g., a
    * pointer) */
 #  define FITS_IN_8_BITS(c) (   (sizeof(c) == 1)                        \
-                             || ((WIDEST_UTYPE)((c) | 0) == ((U8)(c))))
+                 || ((WIDEST_UTYPE) ASSERT_NOT_PTR(c)) == ((U8)(c)))
 #else
 #  define FITS_IN_8_BITS(c) (1)
 #endif