The only purpose of `cmLinkImplItem`'s `FromGenex` member is to decide
whether to check CMP0027. That won't be needed for link items added by
new interfaces in the future. Clarify the name to indicate that we do
not always need to know if the item came from a generator expression.
In commit 7abc3d61ac (Ninja Multi-Config: Fix issue with framework
dependencies and Autogen, 2020-02-13, v3.17.0-rc2~18^2) the `cmLinkItem`
comparison operator was updated to order identical strings by the
cross-config boolean. We need to order identical targets that way too
in order to represent both a cross and non-cross dependency on the same
target.
Issue: #22855
Suppress some cases in `Source/cmGeneratorExpressionNode.cxx` and
`Source/cmUVHandlePtr.h` where a few older compilers require a
user-defined default constructor (with `{}`).
Carry a backtrace on every link item, not just link implementation
items. For now the non-impl items will still have empty backtraces at
runtime, but this will allow us to introduce values over time.
Avoid exposing the item name implicitly as std::string. When the item
is a target, avoid storing a second copy of its name.
Most link item construction is paired with calls to `FindTargetToLink`
to get the possible target pointer. Rename these methods to
`ResolveLinkItem` and refactor them to construct the entire item.
