gdb: Use sighandler_t everywhere

gdb: Use sighandler_t everywhere

This fixes 14 build errors like these in C++ mode:

 src/gdb/extension.c: In function ‘void install_sigint_handler(const signal_handler*)’:
 src/gdb/extension.c:698:41: error: invalid conversion from ‘void (*)()’ to ‘__sighandler_t {aka void (*)(int)}’ [-fpermissive]
    signal (SIGINT, handler_state->handler);
					  ^
 In file included from build-gnulib/import/signal.h:52:0,
		  from ../../src/gdb/extension.c:24:
 /usr/include/signal.h:102:23: error:   initializing argument 2 of ‘void (* signal(int, __sighandler_t))(int)’ [-fpermissive]
  extern __sighandler_t signal (int __sig, __sighandler_t __handler)
			^

Instead of this everywhere:

 -  RETSIGTYPE (*handle_sigint_for_compare) () = handle_sigint;
 +  RETSIGTYPE (*handle_sigint_for_compare) (int) = handle_sigint;

Use sighandler_t (a GNU extension).  That's OK to use unconditionaly
because gnulib's signal.h replacement makes sure that it is available.

gdb/ChangeLog:
2015-08-27  Pedro Alves  <palves@redhat.com>

	* cp-support.c (gdb_demangle): Use sighandler_t.  Remove cast.
	* extension-priv.h: Include signal.h.
	(struct signal_handler) <handler>: Change type to sighandler_t.
	* extension.c (install_gdb_sigint_handler): Use sighandler_t.
	* inflow.c (sigint_ours, sigquit_ours): Change type to
	sighandler_t.
	(child_terminal_inferior): Remove casts.
	(child_terminal_ours_1, new_tty): Use sighandler_t.  Remove casts.
	(osig): Change type to sighandler_t.
	* nto-procfs.c (ofunc): Change type to sighandler_t.
	(procfs_wait): Remove casts.
	* remote-m32r-sdi.c (m32r_wait, m32r_load): Use sighandler_t.
	* remote-sim.c (gdbsim_wait): Use sighandler_t.
	* utils.c (wait_to_die_with_timeout): Use sighandler_t.