RFR: 8293188: x86_64: Introduce stubGenerator_x86_64.hpp [v5]

[Vladimir Ivanov]

> Introduce stubGenerator_x86_64.hpp and extract StubGenerator class declaration there. 
> 
> Testing: hs-tier1 - hs-tier4

Vladimir Ivanov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - update
 - Merge branch 'master' into stub.x86_64.hpp
 - RuntimeStub
 - fix hs-minimal build
 - update
 - fix
 - stubGenerator_x86_64.hpp

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Changes: https://git.openjdk.org/jdk/pull/10111/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10111&range=04
  Stats: 11051 lines in 2 files changed: 3926 ins; 3441 del; 3684 mod
  Patch: https://git.openjdk.org/jdk/pull/10111.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10111/head:pull/10111

PR: https://git.openjdk.org/jdk/pull/10111