[m-rev.] for review: add a note about building the MSVC port on MSYS2

[Julien Fischer]

For review by anyone.

----------------------

Add a note about building the MSVC port on MSYS2.

README.MS-VisualC:
     When using MSVC as the C compiler and building on MSYS2, the
     configuration type must not be "*-pc-msys".  (That configuration
     type is used for building programs for use with MSYS itself, not
     native executables.)

Julien.

diff --git a/README.MS-VisualC b/README.MS-VisualC
index d22f758..b1672f7 100644
--- a/README.MS-VisualC
+++ b/README.MS-VisualC
@@ -35,7 +35,7 @@ do the following:

      or this one to start the MSYS2 shell:

-        C:\> C:\msys32\msys2_shell.cmd -use-full-path
+        C:\> C:\msys64\msys2_shell.cmd -use-full-path -mingw32

      or this one to start the Cygwin shell:

@@ -43,6 +43,11 @@ do the following:

  (We assume the default installation locations for MinGW/MSYS and Cygwin above.)

+Users of MSYS2 should note that it is required that the configuration type
+returned by autoconf match '*mingw*'; in particular it must *not* match
+'*-pc-msys'.  You can use the config.guess script to see what configuration
+type autoconf detects.
+
  In order to install the C#, Erlang or Java grades you will require a C#,
  Erlang or Java compiler to be included in the Windows PATH.
  (See the relevant README files for further details, e.g. README.Java etc)