[crac] RFR: 8273607: Import crac/jdk

[Anton Kozlov]

Import the initial CRaC prototype. The PR targets `crac` branch where it will live, while `master` is automatically synced to `openjdk/master`. The initial implementation is based on jdk-14-ga. After the integration, I'm going to merge the latest promotion build from the `master` branch.

Please feel free to leave comments. I'll try to resolve simple issues or will record more complex ones.

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Commit messages:
 - Update for jcheck
 - Prepare to openjdk/crac
 - Update copyrights
 - Handle non-PID 1 subreaper
 - 8238380: java.base/unix/native/libjava/childproc.c "multiple definition" link errors with GCC10
 - 8238388: libj2gss/NativeFunc.o "multiple definition" link errors with GCC10
 - 8238386: (sctp) jdk.sctp/unix/native/libsctp/SctpNet.c "multiple definition" link errors with GCC10
 - 8237879: make 4.3 breaks build
 - Import crac/jdk a60a8255ccd51ff6d6a2663567769a7c59390e90

Changes: https://git.openjdk.java.net/crac/pull/1/files
 Webrev: https://webrevs.openjdk.java.net/?repo=crac&pr=1&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273607
  Stats: 5558 lines in 95 files changed: 5512 ins; 1 del; 45 mod
  Patch: https://git.openjdk.java.net/crac/pull/1.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/1/head:pull/1

PR: https://git.openjdk.java.net/crac/pull/1