swift234

Re-apply "Fix linkage of 'static inline' Clang-imported definitions"

This re-applies commit r31763 with a change to the predicate we
use for determining the linkage of a definition. It turns out we
could have definitions with a Clang body that were still public,
so instead of checking for a Clang body just check if the Clang
declaration is externally visible or not.

Swift SVN r31777