* doublest.h (DOUBLEST): Use long double only if we can scan

* doublest.h (DOUBLEST): Use long double only if we can scan
it in.  Undefine HAVE_LONG_DOUBLE otherwise.
(DOUBLEST_FORMAT): New.
* c-exp.y (parse_number): Use it.
* jv-exp.y (parse_number): Likewise.
* objc-exp.y (parse_number): Likewise.
* p-exp.y (parse_number): Likewise.
* varobj.c (free_variable): Silence type-punning warnings.
* tui/tui-data.h (struct tui_list): Change type of list member.
* tui/tui-data.c: Remove no-longer-needed type casts.
(source_windows): Silence type-punning warnings.
* tui/tui-stack.c, tui/tui-win.c, tui/tui-winsource.c: Likewise.