[jdk11u-dev] RFR: 8257679: Improved unix compatibility layer in Windows build (winenv) [v11]

[George Adams]

> The main conflict is the lack of the WSL backport ([8215445: Enable building for Windows in WSL](https://github.com/openjdk/jdk/commit/46eb26b692ac7f9431d5b479028ec87e56707557)) Something which doesn't apply particularly cleanly and isn't required to achieve the MSYS2 backport that I'm trying to reach. There are also several Solaris specific edge cases that needed to be rewritten.
> 
> This PR will finally allow me to backport [8287724: Fix various issues with msys2](https://github.com/openjdk/jdk17u-dev/commit/2e21c87fac8d60c3c7ed7b2d0afae9abfc110359) cleanly which should be the final piece in the puzzle to enabling MSYS2 builds.
> 
> @RealCLanger / @GoeLin I suggest that this is run through the full SAP nightlies before this is merged.

George Adams has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  add toolchain changes

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Changes:
  - all: https://git.openjdk.org/jdk11u-dev/pull/1278/files
  - new: https://git.openjdk.org/jdk11u-dev/pull/1278/files/2c4fdab7..f4ba8764

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1278&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1278&range=09-10

  Stats: 12 lines in 1 file changed: 12 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1278.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1278/head:pull/1278

PR: https://git.openjdk.org/jdk11u-dev/pull/1278