cmake: Increase LINK_INTERFACE_MULTIPLICITY of lldbCore

This is necessary to get debug builds of unit tests working on linux.

I think we are at a point where removing dependencies does not prevent
us from depending on the whole world yet. What it does do though, is
make the dependency chains longer as the dependency graph gets sparser,
which means we need to repeat the libraries more times to get the thing
to link.

llvm-svn: 297369