Windows 10 SDK build fixes

Build without Win32.mak, and using Universal C Runtime (UCRT)

windows: Check for APPVER, not VCVER for UCRT

When deciding whether UCRT is used (and thus no CRT merge modules), check for
Windows 10 rather than the version of Visual Studio, as we may be building with
an older SDK.

windows/NTMakefile.sdk

@@ -0,0 +1,128 @@
+########################################################################
+#
+# Copyright (c) 2021, PADL Software Pty Ltd.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# - Redistributions of source code must retain the above copyright
+#   notice, this list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright
+#   notice, this list of conditions and the following disclaimer in
+#   the documentation and/or other materials provided with the
+#   distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN if ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+
+!if !defined(CPU) || "$(CPU)" == ""
+CPU         =AMD64
+!endif
+
+!if "$(CPU)" == "X86" || "$(CPU)" == "x86"
+CPU         =i386
+!endif
+
+!if !defined(APPVER)
+APPVER      =6.1
+!endif
+
+!if "$(APPVER)" == "5.0"
+NMAKE_WINVER=0x0500
+!elseif "$(APPVER)" == "5.01"
+NMAKE_WINVER=0x0501
+!elseif "$(APPVER)" == "5.02"
+NMAKE_WINVER=0x0502
+!elseif "$(APPVER)" == "6.0"
+NMAKE_WINVER=0x0600
+!elseif "$(APPVER)" == "6.1"
+NMAKE_WINVER=0x0601
+!elseif "$(APPVER)" == "10.0"
+NMAKE_WINVER=0x0A00
+!endif
+
+cc          = cl
+link        = link
+implib      = lib
+
+cflags      = -c -DCRTAPI1=_cdecl -DCRTAPI2=_cdecl -nologo -GS -W4
+
+!if "$(CPU)" == "i386"
+cflags      = $(cflags) -D_X86_=1
+!endif
+!if "$(CPU)" == "AMD64"
+cflags      = $(cflags) -D_AMD64_=1
+!endif
+!if "$(CPU)" == "ARM"
+cflags      = $(cflags) -D_ARM_=1
+!endif
+!if "$(CPU)" == "ARM64"
+cflags      = $(cflags) -D_ARM64_=1
+!endif
+
+cflags      = $(cflags) -DWIN32 -D_WIN32
+!if "$(CPU)" == "AMD64" || "$(CPU)" == "ARM64"
+cflags      = $(cflags) -DWIN64 -D_WIN64
+!endif
+
+cflags      = $(cflags) -D_WINNT -D_WIN32_WINNT=$(NMAKE_WINVER)
+cflags      = $(cflags) -DNTDDI_VERSION=$(NMAKE_WINVER)0000
+cflags      = $(cflags) -D_WIN32_IE=$(NMAKE_WINVER) -DWINVER=$(NMAKE_WINVER)
+
+!ifdef NODEBUG
+cdebug      = -Ox -DNDEBUG
+!else
+cdebug      = -Zi -Od -DDEBUG
+!endif
+
+cvarsmt     = -D_MT
+cvarsdll    = -D_MT -D_DLL
+!ifdef NODEBUG
+cvarsmt     = $(cvarsmt) -MTd
+cvarsdll    = $(cvarsdll) -MDd
+!else
+cvarsmt     = $(cvarsmt) -MT
+cvarsdll    = $(cvarsdll) -MD
+!endif
+cvars       = $(cvarsmt)
+
+lflags      = $(lflags) /INCREMENTAL:NO /NOLOGO
+!ifdef NODEBUG
+ldebug      = /RELEASE
+!else
+ldebug      = /DEBUG /DEBUGTYPE:cv
+!endif
+
+!if "$(CPU)" == "i386"
+dllentry    = _DllMainCRTStartup@12
+!else
+dllentry    = _DllMainCRTStartup
+!endif
+
+conlflags   = $(lflags) -subsystem:console,$(APPVER)
+guilflags   = $(lflags) -subsystem:windows,$(APPVER)
+dlllflags   = $(lflags) -entry:$(dllentry) -dll
+
+baselibs    = kernel32.lib ws2_32.lib mswsock.lib advapi32.lib
+conlibs     = $(baselibs)
+conlibsmt   = $(baselibs)
+conlibsdll  = $(baselibs)
+
+winlibs     = $(baselibs) user32.lib gdi32.lib comdlg32.lib winspool.lib
+guilibs     = $(winlibs)
+guilibsmt   = $(winlibs)
+guilibsdll  = $(winlibs)

windows/NTMakefile.w32

@@ -39,7 +39,7 @@ prep::
 
 all:: prep
 
-!include <Win32.Mak>
+!include "NTMakefile.sdk"
 
 !ifdef NODEBUG
 BUILD=rel