"sbt packageBin" fails in cygwin or other windows bash session

 In a Windows SHELL environment, such as cygwin or msys2/mingw64, etc,  Core.settings in project/SparkBuild.scala calls the wrong bash.exe if WSL bash is present (typically at C:\Windows), causing a build failure.  This occurs even though the proper bash.exe is in the PATH ahead of WSL bash.exe.

This is fixed by spark PR 38228

There are 3 parts to the fix, implemented in project/SparkBuild.scala :

• determine the absolute path of the first bash.exe in the command line. 
• determine the build environment (e.g., Linux, Darwin, CYGWIN, MSYS2, etc.)
• For Windows SHELL environments, the first argument to the spawned Process is changed from "bash" to the absolute path.