RFR: 8341831: PhaseCFG::insert_anti_dependences asserts with "no loads"

[Igor Veresov]

`CacheWB` nodes are peculiar in a sense that they both are anti-dependent and produce memory. I think it's reasonable to relax the assert in `insert_anti_dependences()` to work around their properties.

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Commit messages:
 - 8341831: PhaseCFG::insert_anti_dependences asserts with "no loads"

Changes: https://git.openjdk.org/jdk/pull/21455/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21455&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341831
  Stats: 9 lines in 1 file changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21455.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21455/head:pull/21455

PR: https://git.openjdk.org/jdk/pull/21455