[gtkmm/gtkmm-3-24] NMake Makefiles: Use /utf-8 if available

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

commit 31f8b8a5091e427fe02c4ca88af47486fc49e114
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed May 13 11:10:33 2020 +0800

    NMake Makefiles: Use /utf-8 if available
    
    This flag is provided on Visual Studio 2015 and later, so that it will help to
    work around unicode handling issues that occur when building on East Asian
    locales, that is demonstrated by error/warning C4819.
    
    Disabling warning C4828 is meant for gendef.exe, which comes as a consequence
    of using /utf-8.

 MSVC_NMake/config-msvc.mak | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/MSVC_NMake/config-msvc.mak b/MSVC_NMake/config-msvc.mak
index 9dce22d4..444a729e 100644
--- a/MSVC_NMake/config-msvc.mak
+++ b/MSVC_NMake/config-msvc.mak
@@ -128,6 +128,12 @@ GDKMM_BASE_CFLAGS =                \
        /wd4530 /wd4251 /wd4275 \
        /FImsvc_recommended_pragmas.h
 
+!if $(PDBVER) > 14
+GDKMM_BASE_CFLAGS =            \
+       $(GDKMM_BASE_CFLAGS)    \
+       /utf-8 /wd4828  \
+!endif
+
 GTKMM_BASE_CFLAGS =            \
        /Ivs$(PDBVER)\$(CFG)\$(PLAT)    \
        /I..\gtk /I.\gtkmm      \