Fix failure to compile on Windows due to revision 109223.

Fix failure to compile on Windows due to revision 109223.

 src/lisp.h (enum constype): Use CONSTYPE_HEAP and CONSTYPE_PURE for
 enumeration constants, as PURE and HEAP are too general, and clash
 with other headers and sources, such as gmalloc.c and the
 MS-Windows system headers.  All users changed.