Tests such as gc/arguments/TestParallelRefProc.java would fail if GC flag is sent from outside the test using jtreg's vmoptions.
Making the test vm.flagless would prevent it from getting used with other flag combinations. So, it is better to make the test excluded only for GC flag usage.

Currently, this is accomplished by the condition
@requires vm.gc.Serial & vm.gc.G1

The condition is contrived and doesn't read well.
Hence, a new property should be created for this condition.

@requires vm.gc.flagless

PS: This idea can be extended to tests that doesn't sit well with compiler flags.