rust_debug: Cast size_t values to unsigned long before printing.

[CohenArthur]

Using %lu to format size_t values breaks 32 bit targets, and %zu is not
supported by one of the hosts GCC aims to support - HPUX

Fixes #2798

gcc/rust/ChangeLog:

* backend/rust-compile-base.cc (HIRCompileBase::resolve_method_address):
Cast size_t value to unsigned long.
* expand/rust-proc-macro.cc (load_macros): Likewise.
* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): Likewise.

[7Z0t99]

I see that this was already merged, but I still wonder whether this solution is sound on all platforms, because sizeof(unsigned long) < sizeof(size_t) on some platforms, e.g. on win64.

[CohenArthur]

@7Z0t99 you're right that it is unsound, the correct fix would be to use the PRIu64 format specifier. this is a quick and dirty fix as this breaks the build on some GCC targets. it is unsound in that it would display incorrect length values if we have more than UINT32_MAX proc macros at once for example, which is a much bigger issue and shouldn't happen :) these are debug prints anyway and will probably be removed soon.