Add inclusive range support for Rust

Add inclusive range support for Rust

This is version 2 of the patch to add inclusive range support for
Rust.  I believe it addresses all review comments.

Rust recently stabilized the inclusive range feature:

    https://github.com/rust-lang/rust/issues/28237

An inclusive range is an expression like "..= EXPR" or "EXPR ..=
EXPR".  It is like an ordinary range, except the upper bound is
inclusive, not exclusive.

This patch adds support for this feature to gdb.

Regression tested on x86-64 Fedora 27.

2018-04-27  Tom Tromey  <tom@tromey.com>

	PR rust/22545:
	* rust-lang.c (rust_inclusive_range_type_p): New function.
	(rust_range): Handle inclusive ranges.
	(rust_compute_range): Likewise.
	* rust-exp.y (struct rust_op) <inclusive>: New field.
	(DOTDOTEQ): New constant.
	(range_expr): Add "..=" productions.
	(operator_tokens): Add "..=" token.
	(ast_range): Add "inclusive" parameter.
	(convert_ast_to_expression) <case OP_RANGE>: Handle inclusive
	ranges.
	* parse.c (operator_length_standard) <case OP_RANGE>: Handle new
	bounds values.
	* expression.h (enum range_type) <NONE_BOUND_DEFAULT_EXCLUSIVE,
	LOW_BOUND_DEFAULT_EXCLUSIVE>: New constants.
	Update comments.
	* expprint.c (print_subexp_standard): Handle new bounds values.
	(dump_subexp_body_standard): Likewise.

2018-04-27  Tom Tromey  <tom@tromey.com>

	PR rust/22545:
	* gdb.rust/simple.exp: Add inclusive range tests.