Quiet unneeded warning about jdwp

A recent change gave -XjdwpOptions a default value value. This made
the runtime print a (non-fatal) warning if started without jdwp
support telling the user the option is being ignored. Make this
warning only print when the jdwpOptions are explicitly given.

Test: ./art/test/run-test --host --dev 001-HelloWorld
Change-Id: Ie61f3d32462a6b8379d5916ccce37abbc7783d9a
1 file changed