PR go/64836
	PR go/64838

compiler: Use int64_t for backend type size and alignment.

Fixes 32-bit host 64-bit target cross-compilation.

	* go-gcc.cc (Gcc_backend::type_size): Change return type to
	int64_t.
	(Gcc_backend::type_alignment): Likewise.
	(Gcc_backend::type_field_alignment): Likewise.
	(Gcc_backend::type_field_offset): Likewise.
	(Gcc_backend::implicit_variable): Change alignment parameter type
	to int64_t.

From-SVN: r220364