Port to Sun C 5.14

Backport from master.  Sun C 5.14 supports C11 but not GCC
extensions, and so refuses to compile Emacs without this patch.
* src/alloc.c (lmalloc, lrealloc): Don't use INT_ADD_WRAPV on
size_t, as in general this macro is restricted to signed types.

src/alloc.c

@@ -1415,8 +1415,8 @@ lmalloc (size_t size)
       if (laligned (p, size))
 	break;
       free (p);
-      size_t bigger;
-      if (! INT_ADD_WRAPV (size, GCALIGNMENT, &bigger))
+      size_t bigger = size + GCALIGNMENT;
+      if (size < bigger)
 	size = bigger;
     }
 
@@ -1432,8 +1432,8 @@ lrealloc (void *p, size_t size)
       p = realloc (p, size);
       if (laligned (p, size))
 	break;
-      size_t bigger;
-      if (! INT_ADD_WRAPV (size, GCALIGNMENT, &bigger))
+      size_t bigger = size + GCALIGNMENT;
+      if (size < bigger)
 	size = bigger;
     }