RFR: 8306428: RunThese30M.java crashed with assert(early->flag() == current->flag() || early->flag() == mtNone)

[Gerard Ziemski]

Based on Thomas' comments from the bug, we fix it by removing the faulty assert, and instead we handle the case of "**same site, different flags**", as `old site` and `new site`.

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Commit messages:
 - handle sites with differing flags

Changes: https://git.openjdk.org/jdk/pull/14052/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14052&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306428
  Stats: 9 lines in 1 file changed: 7 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14052.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14052/head:pull/14052

PR: https://git.openjdk.org/jdk/pull/14052