patch 9.1.0656: MS-Windows: MSVC Makefile CPU handling can be improved

Problem:  MS-Windows: MSVC Makefile CPU handling can be improved
Solution: Update Makefile and also remove some old code
          (Ken Takata)

* The variable `ASSEMBLY_ARCHITECTURE` was originally used to generate
  the manifest file. However, this was removed in v7.0.198.  Remove
  `ASSEMBLY_ARCHITECTURE` and use `CPU` instead.
* `/arch:AVX512` is available starting from Visual C++ 2017.
* ARM64 was not considered when validating CPUNR.
  Skip the validation for ARM64 for now.
* Remove old code for VC6/7 and Win9x.

closes: #15422

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/GvimExt/Make_mvc.mak b/src/GvimExt/Make_mvc.mak
index 7068d8f..132a584 100644
--- a/src/GvimExt/Make_mvc.mak
+++ b/src/GvimExt/Make_mvc.mak
@@ -19,25 +19,24 @@
 NODEBUG = 1
 !endif
 
-!ifdef PROCESSOR_ARCHITECTURE
-# On Windows NT
-! ifndef CPU
+!ifndef CPU
 CPU = i386
-!  if !defined(PLATFORM) && defined(TARGET_CPU)
+! ifndef PLATFORM
+!  ifdef 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
+!  elseif defined(VSCMD_ARG_TGT_ARCH)
+PLATFORM = $(VSCMD_ARG_TGT_ARCH)
 !  endif
 ! endif
-!else
-CPU = i386
+! ifdef PLATFORM
+!  if ("$(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
 
 !ifdef SDK_INCLUDE_DIR
@@ -80,7 +79,6 @@
 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
 
@@ -96,4 +94,3 @@
 	- 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