Before this cl, blueprint expressions were evaluated as they were
parsed. We want to add a feature to select statements where we can
bind the value of soome value from soong into a blueprint variable,
that then can be used like a regular variable in the .bp file. This
means that select statements need to hold whole unevalated expression
trees, and have the ability to evaluate them later on when the value
of the bound variable is known.
This cl doesn't implement the new select syntax, but it does split
blueprint's parsing and evaluating into two separate stages. We also
store expressions in selects and evaluate them when the select is
resolved.
I didn't do extensive performance evaluation, but a simple comparison
of the time of `touch Android.bp && m nothing` before/after this cl
showed a 1 second speedup. (That was probably just noise)
Bug: 323382414
Test: m nothing --no-skip-soong-tests
Change-Id: I12f373719991afeb4aec76517153f32229d97ff2
1e62c68bfe
