patch 8.1.0128: building with MinGW does not work out-of-the-box

Problem:    Building with MinGW does not work out-of-the-box.
Solution:   Add instructions for MSYS2.  Set default WINVER.  Add batch files
            to set $PATH for MSYS2.
diff --git a/Filelist b/Filelist
index f141dc3..07df299 100644
--- a/Filelist
+++ b/Filelist
@@ -412,6 +412,8 @@
 		src/msvc2008.bat \
 		src/msvc2010.bat \
 		src/msvc2015.bat \
+		src/msys32.bat \
+		src/msys64.bat \
 		src/dimm.idl \
 		src/dlldata.c \
 		src/dosinst.c \