Pacify Oracle Studio re xterm.c

Pacify Oracle Studio re xterm.c

* src/xterm.c (xErrorHandler,  xIOErrorHandler):
New typedefs.
(xm_get_drag_window_1, x_connection_closed): Use them instead of
void *, since the C standard frowns on converting function
pointers to and from void *.  This pacifies Oracle Studio
diagnostics like “warning: assignment type mismatch: pointer to
void "=" pointer to function(pointer to struct _XDisplay {})\
returning int”.
(x_detect_pending_selection_requests, x_had_errors_p): Do not rely
on implicit conversion of a pointer to a bool return value; use !!
instead.  This pacifies Oracle Studio’s “warning: improper
pointer/integer combination: op "="”.
(xim_open_dpy) [HAVE_X11R6 && !HAVE_X11R6_XIM]: Do not use
xim_destroy_callback; configure.ac says “inoue@ainet.or.jp says
Solaris has a bug related to X11R6-style ## XIM support” and
Oracle Studio complains “warning: assignment type mismatch:
pointer to function(pointer to struct _XIC {}, pointer to char,
pointer\ to char) returning void "=" pointer to function(pointer
to struct _XIM {}, pointer to char, pointer to char) returning
void”.