Ensure that we don't call MethodEntered on runtime methods

It was possible we could incorrectly send an instrumentation method
entry event on a runtime method in some circumstances.

NB Several additional patches are required for the instrumentation
trampolines to actually work correctly in all instances.

Test: ./test.py --host
Test: ./test/testrunner/testrunner.py --host --runtime-option=-Xplugin:libtracefast-trampolined.so
Change-Id: Id21c36e4cc0ab70083162fa1d40510f7d823b9a9