support for MSYS2/MinGW64 on Windows;

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/System/mingw.scala	Sat Oct 10 20:31:54 2020 +0200
@@ -0,0 +1,52 @@
+/*  Title:      Pure/System/mingw.scala
+    Author:     Makarius
+
+Support for MSYS2/MinGW64 on Windows.
+*/
+
+package isabelle
+
+
+object MinGW
+{
+  val none: Context = new Context(None)
+  def context(root: Path) = new Context(Some(root))
+
+  def environment: List[(String, String)] =
+    List("PATH" -> "/usr/bin:/bin:/mingw64/bin", "CONFIG_SITE" -> "/mingw64/etc/config.site")
+
+  def environment_prefix: String =
+    (for ((a, b) <- environment) yield Bash.string(a) + "=" + Bash.string(b))
+      .mkString("/usr/bin/env ", " ", " ")
+
+  class Context private[MinGW](val root: Option[Path])
+  {
+    override def toString: String =
+      root match {
+        case None => "MinGW.none"
+        case Some(msys_root) => "MinGW.context(" + msys_root.toString + ")"
+      }
+
+    def bash_command(command: String): String =
+      root match {
+        case None => command
+        case Some(msys_root) =>
+          File.bash_path(msys_root + Path.explode("usr/bin/bash")) +
+            " -c " + Bash.string(environment_prefix + command)
+      }
+
+    def get_root: Path =
+      if (!Platform.is_windows) error("Windows platform required")
+      else if (root.isEmpty) error("Windows platform needs specification of msys root directory")
+      else root.get
+
+    def check
+    {
+      if (Platform.is_windows) {
+        get_root
+        val result = Isabelle_System.bash(bash_command("uname -s")).check
+        if (!result.out.startsWith("MSYS")) error("Bad msys installation " + get_root)
+      }
+    }
+  }
+}

--- a/src/Pure/build-jars	Sat Oct 10 17:26:23 2020 +0200
+++ b/src/Pure/build-jars	Sat Oct 10 20:31:54 2020 +0200
@@ -133,6 +133,7 @@
   src/Pure/System/isabelle_tool.scala
   src/Pure/System/java_statistics.scala
   src/Pure/System/linux.scala
+  src/Pure/System/mingw.scala
   src/Pure/System/numa.scala
   src/Pure/System/options.scala
   src/Pure/System/platform.scala