RFR: 8356647: C2: Excessively strict assert in PhaseIdealLoop::do_unroll

[Marc Chevalier]

This assert seems a bit too tight. See the JBS issue to check the math: the bound of `trip_count` should be `<= 2^31`, while the current bound is ` < (julong)max_juint/2` = floor((2^32-1)/2) = (2^32-2) / 2 = 2^31-1.

-------------

Commit messages:
 - Relax the assert

Changes: https://git.openjdk.org/jdk/pull/25295/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25295&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356647
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25295.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25295/head:pull/25295

PR: https://git.openjdk.org/jdk/pull/25295