Don't ever call materializeAllPermanently during LTO.

To do this, change the representation of lazy loaded functions.

The previous representation cannot differentiate between a function whose body
has been removed and one whose body hasn't been read from the .bc file. That
means that in order to drop a function, the entire body had to be read.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220580 91177308-0d34-0410-b5e6-96231b3b80d8
Fix copy paste comment

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220581 91177308-0d34-0410-b5e6-96231b3b80d8