Make error usable earlier

Make error usable earlier

error (and other exception-throwing functions) are callable from the
first line of captured_main, but the exception printing code will
crash if called before the first call to set_width.  This commit makes
the exception printing code usable from the moment gdb_stderr is set
up.

gdb/ChangeLog:

	* exceptions.c (print_flush): Protect calls to
	target_terminal_ours and wrap_here.