[ORC] Export process symbols in lli-child-target.

We want this behavior for future testing infrastructure anyway, and it may help
with the failure in https://lab.llvm.org/buildbot/#/builders/98/builds/6401:

/b/fuchsia-x86_64-linux/llvm.obj/tools/clang/stage2-bins/bin/lli: warning:
remote mcjit does not support lazy compilation
Finalization error: could not register eh-frame: __register_frame function not
found
/b/fuchsia-x86_64-linux/llvm.obj/tools/clang/stage2-bins/bin/lli: disconnecting