In anticipation of PR #753 getting merged we'll change this back. However until that PR gets merged the old value "BUILD_TESTS" is really needed.

This could be tidied up significantly, and at some point we will want to parse the markdown and generate more appropriate XML - but this is definitely better than nothing.

Generated code changes coming in next commit.

Build tests optimization
Now lite-test added to CTest collection

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.

Change-Id: I17e16fdae6e4d2fb74d178fa5564a609ed58af1d

Change-Id: Ieb7a2c2fbf35bc2a8fa65b915a5ecb68c83863e4

Additional export as "protobuf" package
for importing from other cmake projects

cmake targets that depend on these libraries will automatically have
these include directories.

Change-Id: I75459b8b6562c3ac58fa4b1e4513accdda43ad64

Change-Id: Ifbc415755266ba3d0ffa5661fcd7c7d2e3b32a22

Change-Id: I5049da7449cbada781aa1e23485a336b584802cb

More tests required. Generated code in next commit.

Change-Id: Idecb2e3a5169f7b40d832242c9c10b0eb4325654