As mentioned in the previous commit, we would like to record additional
information in the find-package stack, but we don't have the information
at the point a stack entry is created. This necessitates making the
stack mutable. However, in order to restrict mutation, do not directly
expose the mutable value, and instead arrange for it to be accessible
only via cmFindPackageStackRAII (renamed and extracted from cmMakefile).
This ensures that mutation can only happen while the stack is being
built.
We would like to record additional information in the find-package
stack, but we don't have the information at the point a stack entry is
created. The most sane way to handle this appears to be making the stack
mutable, at least under specific circumstances. To facilitate this, we
need a mutable stack type.
Refactor cmConstStack into cmStack, with the ability to either allow or
forbid mutation of its data. Re-add cmConstStack as a type alias.
This doesn't yet allow mutating cmFindPackageStack, but it's a necessary
step toward being able to do so.
