patch 9.0.0421: MS-Windows makefiles are inconsistently named

Problem:    MS-Windows makefiles are inconsistently named.
Solution:   Use consistent names. (Ken Takata, closes #11088)
diff --git a/src/GvimExt/Make_mvc.mak b/src/GvimExt/Make_mvc.mak
new file mode 100644
index 0000000..4b83f52
--- /dev/null
+++ b/src/GvimExt/Make_mvc.mak
@@ -0,0 +1,98 @@
+# Makefile for GvimExt, using MSVC
+# Options:
+#   DEBUG=yes		Build debug version (for VC7 and maybe later)
+#   CPUARG=		/arch:IA32/AVX/etc, call from main makefile to set
+#   			automatically from CPUNR
+#
+
+TARGETOS = WINNT
+
+!ifndef APPVER
+APPVER = 5.01
+!endif
+!ifndef WINVER
+WINVER = 0x0501
+!endif
+
+!if "$(DEBUG)" != "yes"
+NODEBUG = 1
+!endif
+
+!ifdef PROCESSOR_ARCHITECTURE
+# On Windows NT
+! ifndef CPU
+CPU = i386
+!  if !defined(PLATFORM) && defined(TARGET_CPU)
+PLATFORM = $(TARGET_CPU)
+!  endif
+!  ifdef PLATFORM
+!   if ("$(PLATFORM)" == "x64") || ("$(PLATFORM)" == "X64")
+CPU = AMD64
+!   elseif ("$(PLATFORM)" == "arm64") || ("$(PLATFORM)" == "ARM64")
+CPU = ARM64
+!   elseif ("$(PLATFORM)" != "x86") && ("$(PLATFORM)" != "X86")
+!    error *** ERROR Unknown target platform "$(PLATFORM)". Make aborted.
+!   endif
+!  endif
+! endif
+!else
+CPU = i386
+!endif
+
+!ifdef SDK_INCLUDE_DIR
+!include $(SDK_INCLUDE_DIR)\Win32.mak
+!elseif "$(USE_WIN32MAK)"=="yes"
+!include <Win32.mak>
+!else
+cc = cl
+link = link
+rc = rc
+cflags = -nologo -c
+lflags = -incremental:no -nologo
+rcflags = /r
+olelibsdll = ole32.lib uuid.lib oleaut32.lib user32.lib gdi32.lib advapi32.lib
+!endif
+
+# include CPUARG
+cflags = $(cflags) $(CPUARG)
+
+# set WINVER and _WIN32_WINNT
+cflags = $(cflags) -DWINVER=$(WINVER) -D_WIN32_WINNT=$(WINVER)
+
+!if "$(CL)" == "/D_USING_V110_SDK71_"
+rcflags = $(rcflags) /D_USING_V110_SDK71_
+!endif
+
+SUBSYSTEM = console
+!if "$(SUBSYSTEM_VER)" != ""
+SUBSYSTEM = $(SUBSYSTEM),$(SUBSYSTEM_VER)
+!endif
+
+!if "$(CPU)" == "AMD64" || "$(CPU)" == "ARM64"
+OFFSET = 0x11C000000
+!else
+OFFSET = 0x1C000000
+!endif
+
+all: gvimext.dll
+
+gvimext.dll:    gvimext.obj	\
+		gvimext.res
+	$(link) $(lflags) -dll -def:gvimext.def -base:$(OFFSET) -out:$*.dll $** $(olelibsdll) shell32.lib comctl32.lib -subsystem:$(SUBSYSTEM)
+	if exist $*.dll.manifest mt -nologo -manifest $*.dll.manifest -outputresource:$*.dll;2
+
+gvimext.obj: gvimext.h
+
+.cpp.obj:
+	$(cc) $(cflags) -DFEAT_GETTEXT $(cvarsmt) $*.cpp
+
+gvimext.res: gvimext.rc
+	$(rc) /nologo $(rcflags) $(rcvars)  gvimext.rc
+
+clean:
+	- if exist gvimext.dll del gvimext.dll
+	- if exist gvimext.lib del gvimext.lib
+	- if exist gvimext.exp del gvimext.exp
+	- if exist gvimext.obj del gvimext.obj
+	- if exist gvimext.res del gvimext.res
+	- if exist gvimext.dll.manifest del gvimext.dll.manifest