Move constants into the right file.

Document them while we're moving them.

src/mem/allocconfig.h

@@ -4,12 +4,6 @@
 
 namespace snmalloc
 {
-  enum ZeroMem
-  {
-    NoZero,
-    YesZero
-  };
-
   // 0 intermediate bits results in power of 2 small allocs. 1 intermediate
   // bit gives additional sizeclasses at the midpoint between each power of 2.
   // 2 intermediate bits gives 3 intermediate sizeclasses, etc.

src/pal/pal_consts.h

@@ -27,4 +27,19 @@ namespace snmalloc
      */
     AlignedAllocation = (1 << 1)
   };
+  /**
+   * Flag indicating whether requested memory should be zeroed.
+   */
+  enum ZeroMem
+  {
+    /**
+     * Memory should not be zeroed, contents are undefined.
+     */
+    NoZero,
+    /**
+     * Memory must be zeroed.  This can be lazily allocated via a copy-on-write
+     * mechanism as long as any load from the memory returns zero.
+     */
+    YesZero
+  };
 }