Fix lib/common objs not included in lib/gvc lib for CMake builds

Fix lib/common objs not included in lib/gvc lib for CMake builds

This is what the autotools builds do.

For some reason this was not a problem on Windows.

Without this, the rtest/test_examples.py gave errors like this for e.g. demo.c:

demo.c:(.text+0x29): undefined reference to `gvParseArgs'