[REDO] C1/C2 compiler support for blackholes

This is redo of JDK-8252505.

JMH uses the Blackhole::consume() methods to avoid dead-code elimination of the code that produces benchmark values. It now relies on producing opaque side-effects and breaking inlining:
  https://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-core/src/main/java/org/openjdk/jmh/infra/Blackhole.java#l153

While it was proved useful for many years, it unfortunately comes with several major drawbacks:
 
 1. Call costs dominate nanobenchmarks. On TR 3970X, the call cost is several nanoseconds.
 2. The work spent in Blackhole.consume dominates nanobenchmarks too. It takes about a nanosecond on TR 3970X.
 3. Argument preparation for call makes different argument types behave differently. This is prominent on architectures where calling conventions for passing e.g. floating-point arguments require elaborate dance.

Supporting this directly in compilers would improve nanobenchmark fidelity.

Instead of introducing public APIs, we can hook a new command to compiler control, and let JMH sign up its Blackhole methods for it with -XX:CompileCommand=blackhole,org.openjdk.jmh.infra.Blackhole::consume. This is being prototyped as CODETOOLS-7902762.

Dirty C1/C2 prototype that handles all arguments to "blackholed" method:
  https://github.com/openjdk/jdk/pull/2024

It makes Blackholes behave substantially better:
 http://cr.openjdk.java.net/~shade/8252505/bh-old-vs-new.png