[wide-int] fix 32-bit x86 builds

[Mike Stump]

We changed the underlying type a while back, and it matters on 32-bit pointer 
machines that use long long for a HOST_WIDE_INT…  Caught by fold-checking, 
thanks fold checking.

Checked in as obvious.

Index: tree.c
===================================================================
--- tree.c      (revision 209928)
+++ tree.c      (working copy)
@@ -1959,7 +1959,7 @@ tree
 make_int_cst_stat (int len, int ext_len MEM_STAT_DECL)
 {
   tree t;
-  int length = (ext_len - 1) * sizeof (tree) + sizeof (struct tree_int_cst);
+  int length = (ext_len - 1) * sizeof (HOST_WIDE_INT) + sizeof (struct 
tree_int_cst);
 
   gcc_assert (len);
   record_node_allocation_statistics (INTEGER_CST, length);