RFR: 8280593: [PPC64, S390] redundant allocation of MacroAssembler in StubGenerator ctor [v3]

[Richard Reingruber]

> This cleanup removes a redundant allocation from the StubGenerator constructor. The base class' constructor does the very same.
> 
> The fix passed our CI testing.

Richard Reingruber has updated the pull request incrementally with one additional commit since the last revision:

  Update copyright year.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7215/files
  - new: https://git.openjdk.java.net/jdk/pull/7215/files/dd330af6..658104ed

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7215&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7215&range=01-02

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7215.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7215/head:pull/7215

PR: https://git.openjdk.java.net/jdk/pull/7215