Change functions in cp-name-parser.y into methods

Pedro pointed out in an earlier patch that it would be possible to
make some helper functions in cp-name-parser.y into methods on
cpname_state, cleaning up the code a bit.  This patch implements this
idea.

Doing this required moving the %union earlier in the .y file, so the
patch is somewhat bigger than you might expect.

Tested by building with both bison and byacc, and then running the
gdb.cp tests.

gdb/ChangeLog
2018-06-04  Tom Tromey  <tom@tromey.com>

	* cp-name-parser.y (cpname_state): Add method declarations.
	(HANDLE_QUAL): Update.
	(cpname_state::d_grab, cpname_state::fill_comp)
	(cpname_state::make_operator, cpname_state::make_dtor)
	(cpname_state::make_builtin_type, cpname_state::make_name)
	(cpname_state::d_qualify, cpname_state::d_int_type)
	(cpname_state::d_unary, cpname_state::d_binary): Now methods.
	(%union): Move earlier.