RFR: 8293188: x86_64: Introduce stubGenerator_x86_64.hpp [v4]

[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 incrementally with one additional commit since the last revision:

  RuntimeStub

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10111/files
  - new: https://git.openjdk.org/jdk/pull/10111/files/93b6ddee..31a8683f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10111&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10111&range=02-03

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 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