RFR: 8238669: Long.divideUnsigned is extremely slow for certain values (Needs to be Intrinsic)

[rgiulietti]

This is a follow-up of the Mercurial-based workflow initiated on the core-lib-devs mailing list [0]. Not sure if this
one is strictly necessary or if the patches sent on the list are sufficient. Anyway, I exploit this PR as a test ;-)

[0] https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-September/068474.html

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Commit messages:
 - 8238669: Long.divideUnsigned is extremely slow for certain values (Needs to be Intrinsic)

Changes: https://git.openjdk.java.net/jdk/pull/31/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=31&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238669
  Stats: 73 lines in 2 files changed: 32 ins; 15 del; 26 mod
  Patch: https://git.openjdk.java.net/jdk/pull/31.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/31/head:pull/31

PR: https://git.openjdk.java.net/jdk/pull/31