Modular Codegen: Don't home always_inline functions

Since they'll likely (not always - if the address is taken, etc) be
inlined away, even at -O0, separately provided weak definitions are
likely to be unused so skip all of that.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@317279 91177308-0d34-0410-b5e6-96231b3b80d8