RFR: 8366837: Clean up gensrc by spp.Spp

[Magnus Ihse Bursie]

Several java classes in java.base is generated from templates using SPP, the "Stream Preprocessor". Unfortunately much of this code is very old and has survived unchanged since pre-JDK 7. It does not follow modern makefile standards for abstraction, safe coding practices, etc. In short, they have been a thorn in the side for a long time, and the time has finally come to clean them up.

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

Commit messages:
 - Fix syntax error
 - Don't use $(if ...) for KEYS.
 - Move weird characters in template expansion from command line to the template itself
 - Merge branch 'master' into cleanup-spp-gensrc
 - 8366837: Clean up gensrc by spp.Spp

Changes: https://git.openjdk.org/jdk/pull/27078/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27078&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366837
  Stats: 1321 lines in 9 files changed: 523 ins; 562 del; 236 mod
  Patch: https://git.openjdk.org/jdk/pull/27078.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27078/head:pull/27078

PR: https://git.openjdk.org/jdk/pull/27078