RFR: 8304888: Add dedicated VMProps for linker and fallback linker [v2]

[Jorn Vernee]

> This patch adds a dedicated jtreg property to check which CABI is being used by the JDK, which can be used both to check whether the foreign linker is supported, and whether the fallback linker is being used. (and, possibly it can also be use to check for a particular ABI in case we want to add ABI specific tests).
> 
> Checking whether the foreign linker is supported currently requires using an unwieldy expression that checks if we are running on a platform that has a foreign linker port. Checking for the fallback linker currently uses `vm.flavor != "zero"` which is not always correct, since the fallback linker can also be used on other platforms which are not `zero`.
> 
> To initialize the property, VMProps directly reads `jdk.internal.foreig.CABI::current()`. Since this class is in an internal package, `--add-exports` flags are added as javac flags and VM flags for the extra prop definitions class.

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 43 commits:

 - use only jdk.CABI property
 - use extra props to check for linker
 - Add fallbackLinker vmprop
 - Merge pull request #3 from JornVernee/IsForeignLinkerSupported
   
   rename has_port
 - rename has_port
 - Merge pull request #2 from JornVernee/WSL_BB
   
   account for missing functional in WSL in TestByteBuffer
 - account for missing mincore on WSL in TestByteBuffer
 - Merge branch 'master' into PR_21_V2
 - 8305369: Issues in zero-length memory segment javadoc section
 - 8305087: MemoryLayout API checks should be more eager
 - ... and 33 more: https://git.openjdk.org/jdk/compare/d8af7a60...aa90690c

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Changes: https://git.openjdk.org/jdk/pull/13429/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13429&range=01
  Stats: 13516 lines in 285 files changed: 5119 ins; 6185 del; 2212 mod
  Patch: https://git.openjdk.org/jdk/pull/13429.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13429/head:pull/13429

PR: https://git.openjdk.org/jdk/pull/13429