x86_32 builds fail after JDK-8253180

* For target hotspot_variant-server_libjvm_objs_c2_safepointPollStubTable_x86.o:
/home/buildbot/worker/build-jdkX-linux/build/src/hotspot/cpu/x86/c2_safepointPollStubTable_x86.cpp: In member function 'void C2SafepointPollStubTable::emit_stub_impl(MacroAssembler&, C2SafepointPollStubTable::C2SafepointPollStub*) const':
/home/buildbot/worker/build-jdkX-linux/build/src/hotspot/cpu/x86/c2_safepointPollStubTable_x86.cpp:43:21: error: 'r15_thread' was not declared in this scope
   __ movptr(Address(r15_thread, JavaThread::saved_exception_pc_offset()), rscratch1);