Fix TestStubSetSID after unification in to a single lldb-server binary.

Summary:
lldb-server needs an explicit 'g' or 'p' argument now. Since lldb-server
is started as a gdbserver in this test, 'g' should be passed to it
explicitly.

Test Plan: ./dotest.py -p TestStubSetSID

Reviewers: flackr, ovyalov

Reviewed By: ovyalov

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D7801

llvm-svn: 230082