tril tests are not able to detect the right CPU level on Z

[dchopra001]

Removing a SKIP_ON_S390 check like the one below:
https://github.com/eclipse/omr/blob/149b5245ac056f5025d141760ea995822fc30c74/fvtest/compilertriltest/VectorTest.cpp#L313-L322

Results in Assertion failures on Z:

Assertion failed at /home/dchopra/openj9-openjdk-jdk17/omr/compiler/z/codegen/OMRInstruction.cpp:89:() cg->comp()->target().cpu.isAtLeast(_opcode.getMinimumALS())
	Processor detected (Unknown) does not support instruction VL

It looks like the processor is not detected properly. This is most likely happening because we call the default constructor for OMRCPU here:
https://github.com/eclipse/omr/blob/0d4b2da9e86466d10e8f9a77cc3521c4b9548341/compiler/z/env/OMRCPU.cpp#L34-L42

The call to detect is made here:
https://github.com/eclipse/omr/blob/149b5245ac056f5025d141760ea995822fc30c74/fvtest/compilertriltest/VectorTest.cpp#L327-L331

Is privateOmrPortLibrary expected to be null here?