compiler: Report errors from very large types.

compiler: Report errors from very large types.

    The gcc backend throws an internal error when trying to get the size
    of a type which is larger than the amount of address space on the
    machine.  This patch catches this error and reports it in a user
    friendly way.

    Fixes golang/go#11554.

    Reviewed-on: https://go-review.googlesource.com/13684

	* go-gcc.cc (Gcc_backend::type_size): Return -1 for
	unrepresentable size.

From-SVN: r227656