Switch the linker to having a whitelist of GVs.

This replaces DoNotLinkFromSource with ValuesToLink. It also moves the
computation of ValuesToLink earlier.

It is a bit simpler and an important step in slitting the linker into an
ir mover and a linker proper.

The test change is because we now avoid creating dead declarations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254559 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed