RFR: L/Q again, step two

[Frederic Parain]

Please review this second set of fixes for the L/Q transition.
A few changes in C1, most changes in CI.
CI always delegates to the runtime to know if a null-free array is flattened or not (to avoid duplication of the flattening decision code).

With those changes, all tests in runtime/valhalla/inlinetypes now pass with -Xcomp -XX:TieredStopAtLevel=1 (at least on Linux x64).
Some tests in compiler/valhalla/inlinetypes still fail but they will require more time to be investigated (some tests force use of C2 or expect code to be C2 compiled, but C2 is not fixed yet).

Thank you,

Fred

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Commit messages:
 - Remove useless statement
 - Merge remote-tracking branch 'upstream/lqagain' into lq_steptwo
 - Second set of fixes, focus on CI/C1

Changes: https://git.openjdk.java.net/valhalla/pull/414/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=414&range=00
  Stats: 62 lines in 11 files changed: 41 ins; 4 del; 17 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/414.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/414/head:pull/414

PR: https://git.openjdk.java.net/valhalla/pull/414