[glibmm/glibmm-2-62] NMake Makefiles: Use /utf-8 where available

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

commit fa989d1ac25460c8d1f3cf9cc8eb6d024dba473d
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Thu Dec 26 17:58:04 2019 +0800

    NMake Makefiles: Use /utf-8 where available
    
    This avoids miscompilations under certain locales (Chinese, Japanese and
    Korean in particular) where Unicode sequences are not properly handled
    by the Visual Studio compiler.

 MSVC_NMake/detectenv-msvc.mak | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/MSVC_NMake/detectenv-msvc.mak b/MSVC_NMake/detectenv-msvc.mak
index 9a92c110..754080ad 100644
--- a/MSVC_NMake/detectenv-msvc.mak
+++ b/MSVC_NMake/detectenv-msvc.mak
@@ -122,6 +122,10 @@ CFLAGS_ADD = $(CFLAGS_ADD_NO_GL) /GL
 !if "$(VSVER)" != "9"
 CFLAGS_ADD = $(CFLAGS_ADD) /d2Zi+
 CFLAGS_ADD_NO_GL = $(CFLAGS_ADD_NO_GL) /d2Zi+
+!if $(VSVER) >= 14
+CFLAGS_ADD = $(CFLAGS_ADD) /utf-8
+CFLAGS_ADD_NO_GL = $(CFLAGS_ADD_NO_GL) /utf-8
+!endif
 !endif
 !else
 CFLAGS_ADD = /MDd /Od