RFR(XXS): 8221483: TestOopCmp.java fails due to "Multiple garbage collectors selected"

[Volker Simonis]

Hi,

sorry, but I broke tier 3 suite with my test from "8221083 [ppc64]
Wrong oop compare in C1-generated code". The fix is trivial:

http://cr.openjdk.java.net/~simonis/webrevs/2019/8221483/
https://bugs.openjdk.java.net/browse/JDK-8221483

Because the test is only meaningful if run with SerialGC it uses
"main/othervm" mode with "-XX:+UseSerialGC" as command line option.
However this may break if JTreg is called with another, explicit GC
setting in "vmoptions" (what the tier3 tests are apparently doing).

Adding "@requires vm.gc.Serial" will only run the test if no explicit
GC was set outside of the test or if the GC was explicitly set to
"UseSerial".

Thanks,
Volker