further clarify that Msys2 is a fork of Cygwin

CHANGES

@@ -1,3 +1,10 @@
+The following are the changes from calc version 2.14.3.5 to date:
+
+    As Msys2 is a fork of Cygwin, if the OSNAME is Msys, the Cygwin
+    target will be used.  Thanks to GitHub user @iahung2 for the
+    pull request.
+
+
 The following are the changes from calc version 2.14.3.4 to 2.14.3.5:
 
     Under macOS, to reduce dependency chains, we remove functions

HOWTO.INSTALL

@@ -271,7 +271,7 @@ The current list of targets in Makefile.target are:
 - Apple macOS / Darwin target
 - FreeBSD target
 - OpenBSD target
-- Cygwin target
+- Cygwin target (as well as Msys2 / Msys OSNAME)
 - simple target
 - default target (when target is empty)
 

Makefile.config

@@ -99,12 +99,13 @@ endif	# ($(target),Darwin)
 # If you are using Cygwin with MinGW64 packages
 # then we will also need to use the Cygwin runtime enviroment
 # and the calc Cygwin make target.
-##
+#
 ifeq ($(OSNAME),Cygwin)
 target:= Cygwin
 endif	# ($(OSNAME),Cygwin)
 
 # MSYS2 (MSYS) is a fork of Cygwin
+#
 ifeq ($(OSNAME),Msys)
 target:= Cygwin
 endif	# ($(OSNAME),Msys)