RFR: 7903738 : jtr.xml logs produced with -xml argument do not contain compilation failure justification

[andrlos]

jtr.xml files generated while using -xml flag don't contain any info about why the compilation failed although the info is present in jtr files. This can be solved by looking for the compilation failure in case there is no main section -> the main has not been executed -> failure occurred during compilation

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Commit messages:
 - revision after review
 - cosmetic edits
 - compilation errors now also written in xml logs

Changes: https://git.openjdk.org/jtreg/pull/229/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=229&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903738
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jtreg/pull/229.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/229/head:pull/229

PR: https://git.openjdk.org/jtreg/pull/229