RFR: 8316879: RegionMatches1Tests fails if CompactStrings are disabled after JDK-8302163 [v6]

[Aleksei Voitylov]

> test java.lang.String.RegionMatches1Tests fails on all platforms with -XX:-CompactStrings option and on ARM32 where Compact Strings is disabled by default. The fix is to return true immediately if len is negative, since for negative length this condition will never be satisfied.
> 
> Testing: JCK, JTREG passed with the fix with -XX:-CompactStrings on x86_64 and on ARM32.

Aleksei Voitylov has updated the pull request incrementally with one additional commit since the last revision:

  address review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15906/files
  - new: https://git.openjdk.org/jdk/pull/15906/files/caaa99db..aa5faeac

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15906&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15906&range=04-05

  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15906.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15906/head:pull/15906

PR: https://git.openjdk.org/jdk/pull/15906