RFR: 8268174: Move x86-specific stub declarations into stubRoutines_x86.hpp [v2]

[Vladimir Ivanov]

> A cleanup which makes x86-specific stubs platform-specific.
> 
> Testing:
> - [x] hs-tier1 - hs-tier2
> - [x] x86_32 hotspot build

Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  New line

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4335/files
  - new: https://git.openjdk.java.net/jdk/pull/4335/files/a790e59e..140f2c34

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4335&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4335&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4335.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4335/head:pull/4335

PR: https://git.openjdk.java.net/jdk/pull/4335