When trying to compile the protobuf code as a DLL, and then compile other DLLs
with generated .pb.cc/h files that reference
InternalMetadataWithArena::InternalMetadataWithArena(Arena*), MSVC gives an
"unresolved external symbol" error. This seems to be due to the function being
simultaneously exported and inline. Moving it out-of-line fixes things.
There are other functions exported and inline as well but de-inlining them
doesn't seem to be necessary to get the build working, and I'd rather de-inline
as few functions as possible.
Dennis Cappendijk
Konstantin Podsvirov
Peter Kasting
Bo Yang
Jisi Liu
Tom Hughes
Feng Xiao