Update gdb test suite for Rust

Update gdb test suite for Rust

This updates the gdb test suite for Rust.

2016-05-17  Tom Tromey  <tom@tromey.com>
	    Manish Goregaokar <manishsmail@gmail.com>

	* lib/rust-support.exp: New file.
	* lib/gdb.exp (skip_rust_tests): New proc.
	(build_executable_from_specs): Handle rust.
	* lib/future.exp (gdb_find_rustc): New proc.
	(gdb_default_target_compile): Handle rust.
	* gdb.rust/expr.exp: New file.
	* gdb.rust/generics.exp: New file.
	* gdb.rust/generics.rs: New file.
	* gdb.rust/methods.exp: New file.
	* gdb.rust/methods.rs: New file.
	* gdb.rust/modules.exp: New file.
	* gdb.rust/modules.rs: New file.
	* gdb.rust/simple.exp: New file.
	* gdb.rust/simple.rs: New file.