[ORC] Exclude RemoteObjectLayer from the ExecutionEngine module, as modules

builds seem to be having trouble with it.

http://lab.llvm.org:8011/builders/clang-x86_64-linux-selfhost-modules-2/builds/11401

When trying to link lli-child-target, the linker reports missing symbols for
the 'Name' members of 'rpc::Function<OrcRPCNegotiate, FunctionIdT(std::string)>'
(base class for OrcRPCNegotiate) and 'rpc::Function<OrcRPCResponse, void()>'
(base class for OrcRPCResponse), despite there being definitions for these
immediately below the rpc::Function class template.

This looks like the same bug that bit OrcRemoteTargetClient/Server in r286920.

<rdar://problem/34249745>

llvm-svn: 312515