[glibmm/glibmm-2-64] NMake Makefiles: Support ARM64 Windows builds

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

commit c0cd971dc585dd2db2981aa264ad98b0a15d5fc1
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed Jul 8 16:07:52 2020 +0800

    NMake Makefiles: Support ARM64 Windows builds
    
    This will make the NMake Makefiles capable of building ARM64 binaries of glibmm
    and giomm, which can be used on Windows 10 on ARM systems.

 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 c59e0299..f2fa09cf 100644
--- a/MSVC_NMake/detectenv-msvc.mak
+++ b/MSVC_NMake/detectenv-msvc.mak
@@ -68,6 +68,8 @@ _HASH=^#
     && ![echo PLAT=Win32 >> vercl.x] \
     && ![echo $(_HASH)elif defined(_M_AMD64) >> vercl.x] \
     && ![echo PLAT=x64 >> vercl.x] \
+    && ![echo $(_HASH)elif defined(_M_ARM64) >> vercl.x] \
+    && ![echo PLAT=arm64 >> vercl.x] \
     && ![echo $(_HASH)endif >> vercl.x] \
     && ![cl -nologo -TC -P vercl.x $(ERRNUL)]
 !include vercl.i
@@ -145,6 +147,8 @@ CFLAGS_ADD_NO_GL = $(CFLAGS_ADD)
 
 !if "$(PLAT)" == "x64"
 LDFLAGS_ARCH = /machine:x64
+!elseif "$(PLAT)" == "arm64"
+LDFLAGS_ARCH = /machine:arm64
 !else
 LDFLAGS_ARCH = /machine:x86
 !endif