borrowck: Avoid overloading issues on 32bit architectures

borrowck: Avoid overloading issues on 32bit architectures

On architectures where `size_t` is `unsigned int`, such as 32bit x86,
we encounter an issue with `PlaceId` and `FreeRegion` being aliases to
the same types. This poses an issue for overloading functions for these
two types, such as `push_subset` in that case. This commit renames one
of these `push_subset` functions to avoid the issue, but this should be
fixed with a newtype pattern for these two types.

gcc/rust/ChangeLog:

	* checks/errors/borrowck/rust-bir-fact-collector.h (points): Rename
	`push_subset(PlaceId, PlaceId)` to `push_subset_place(PlaceId, PlaceId)`