updated MinGW installation: requires Cygwin from Isabelle2018 to avoid problems with address relocation;

--- a/Admin/polyml/INSTALL-MinGW	Thu Nov 14 11:40:55 2019 +0100
+++ b/Admin/polyml/INSTALL-MinGW	Thu Nov 14 11:43:46 2019 +0100
@@ -3,29 +3,19 @@
 
 - always "Run as administrator ..."
 
-- http://sourceforge.net/projects/msys2
-
-  target c:\msys64
-
-- http://sourceforge.net/projects/mingw-w64
+- download from https://www.msys2.org
+  install target c:\msys64
 
-  mingw-w64-install.exe
+- package update and installation within msys2 shell:
 
-  i686-4.9.3-win32-dwarf-rt_v4-rev0
-  x86_64-4.9.3-win32-seh-rt_v4-rev0
-
-  target c:\msys64
+  pacman -Syuu
 
-- within msys shell:
+  pacman -Su
 
-    pacman --needed -Sy bash pacman pacman-mirrors msys2-runtime
-
-  after restart of msys shell:
+  pacman -S --needed base-devel gmp-devel mingw-w64-x86_64-toolchain mingw-w64-x86_64-gmp
 
-    pacman -Su
-    pacman -S make diffutils texinfo gmp-devel mingw-w64-i686-gmp mingw-w64-x86_64-gmp
+- build (as regular user) e.g. on vmnipkow9 with Cygwin-Terminal from Isabelle2018
+  (to avoid address relocation problems):
 
-- build (as regular user) e.g. on vmnipkow9
-
-  isabelle/repos/Admin/polyml/build polyml-git x86-windows --build=i686-pc-msys --with-gmp
-  isabelle/repos/Admin/polyml/build polyml-git x86_64-windows --build=x86_64-pc-msys --with-gmp
+    isabelle build_polyml -M /cygdrive/c/msys64 -m32 -s sha1 src
+    isabelle build_polyml -M /cygdrive/c/msys64 -m64 -s sha1 src

--- a/src/Pure/Admin/build_polyml.scala	Thu Nov 14 11:40:55 2019 +0100
+++ b/src/Pure/Admin/build_polyml.scala	Thu Nov 14 11:43:46 2019 +0100
@@ -39,11 +39,12 @@
           List("--host=x86_64-w64-mingw32", "CPPFLAGS=-I/mingw64/include", "--disable-windows-gui"),
         setup =
           """PATH=/usr/bin:/bin:/mingw64/bin
-            export CONFIG_SITE=/etc/config.site""",
+            export CONFIG_SITE=/mingw64/etc/config.site""",
         copy_files =
           List("$MSYS/mingw64/bin/libgcc_s_seh-1.dll",
             "$MSYS/mingw64/bin/libgmp-10.dll",
-            "$MSYS/mingw64/bin/libstdc++-6.dll")))
+            "$MSYS/mingw64/bin/libstdc++-6.dll",
+            "$MSYS/mingw64/bin/libwinpthread-1.dll")))
 
   def build_polyml(
     root: Path,