CMake: Eliminate unused checks and #undef(s) as below;

STACK_DIRECTION
YYTEXT_POINTER
HAVE_NAMESPACES
HAVE_STD_ITERATOR
HAVE_FWD_ITERATOR
HAVE_BI_ITERATOR
HAVE_GLOBAL_HASH_MAP
HAVE_GLOBAL_HASH_SET
HAVE_GNU_EXT_HASH_MAP
HAVE_GNU_EXT_HASH_SET
HAVE_STD_EXT_HASH_MAP
HAVE_STD_EXT_HASH_SET

llvm-svn: 137423