[modules] When we see a definition of a function for which we already have a

[modules] When we see a definition of a function for which we already have a
non-visible definition, skip the new definition to avoid ending up with a
function with multiple definitions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245664 91177308-0d34-0410-b5e6-96231b3b80d8