[atkmm] NMake Makefiles: Disable warnings C4251 and C4275

[Chun-wei Fan <fanchunwei src gnome org>]

commit 334337ba57f92c24e372a93bf2c72e029d76e889
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed Apr 1 12:32:09 2020 +0800

    NMake Makefiles: Disable warnings C4251 and C4275
    
    Since we are building against GLib that use __declspec(dllimport) to
    import symbols, we can safely ignore warnings C4251 and C4275, as they
    are harmless in this case as we are certain that we are really using
    those compiler directives.

 MSVC_NMake/config-msvc.mak | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/MSVC_NMake/config-msvc.mak b/MSVC_NMake/config-msvc.mak
index ff5a62b..ab4a66e 100644
--- a/MSVC_NMake/config-msvc.mak
+++ b/MSVC_NMake/config-msvc.mak
@@ -24,7 +24,8 @@ DEBUG_SUFFIX =
 
 ATKMM_BASE_CFLAGS =            \
        /I..\atk /I.\atkmm      \
-       /wd4530 /std:c++17      \
+       /wd4530 /wd4251 \
+       /wd4275 /std:c++17      \
        /utf-8  \
        /FImsvc_recommended_pragmas.h