RFR: 8284848: C2: Compiler blackhole arguments should be treated as globally escaping

[Aleksey Shipilev]

WIP so far, but I would appreciate early review of someone savvy in C2 EA code. I'll try to whip up the test with IR Framework too.

See more discussion in the bug.

Additional testing:
 - [x] Linux x86_64 fastdebug `tier1`
 - [x] Linux x86_64 fastdebug `tier2`
 - [x] OpenJDK microbenchmark corpus sanity run

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/8228/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8228&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284848
  Stats: 26 lines in 1 file changed: 26 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8228.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8228/head:pull/8228

PR: https://git.openjdk.java.net/jdk/pull/8228