test: detect missing postmortem metadata
This commit updates test-postmortem-metadata to provide a more useful error message in the scenario where Node is compiled without postmortem support.
Refs: https://github.com/nodejs/node/pull/27375#issuecomment-494869011
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines