config.sub: Accept LLVM-style $cpu-$vendor-windows-{gnu,msvc}

In older times, MinGW (GCC toolchain with modified windows headers) was
the only free software toolchain for Windows.  But now, LLVM has support
both for MinGW ABI and Microsoft's own.  The distinction matters for C++
more than C.

LLVM[1], Rust[2], and other projects have taken to differentiating these
two as `...windows-gnu` vs `...windows-msvc`.  I think that makes a lot
of sense, as it correctly identifiers both their commonalities and their
differences.

A lot of MinGW-supporting software, most notably GCC itself, will
presumably continue to use configs like x86_64-pc-mingw32 and
i686-pc-mingw32.  That's fine; this patch doesn't normalize them away
(like LLVM does) or remove them!  If and when that software wants to
support the MSVC ABI without requiring MSVC itself, they can switch to
these newer configurations.

[1]: a18266473b/llvm/unittests/TargetParser/TripleTest.cpp (L1907-L1951)
[2]: 36fb58e433/compiler/rustc_target/src/spec/mod.rs (L1255-L1271)

config.sub

@@ -4,7 +4,7 @@
 
 # shellcheck disable=SC2006,SC2268 # see below for rationale
 
-timestamp='2023-06-23'
+timestamp='2023-06-26'
 
 # This file is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License as published by
@@ -145,7 +145,8 @@ case $1 in
 			nto-qnx* | linux-* | uclinux-uclibc* \
 			| uclinux-gnu* | kfreebsd*-gnu* | knetbsd*-gnu* | netbsd*-gnu* \
 			| netbsd*-eabi* | kopensolaris*-gnu* | cloudabi*-eabi* \
-			| storm-chaos* | os2-emx* | rtmk-nova* | managarm-*)
+			| storm-chaos* | os2-emx* | rtmk-nova* | managarm-* \
+			| windows-* )
 				basic_machine=$field1
 				basic_os=$maybe_os
 				;;
@@ -1766,7 +1767,7 @@ case $os in
 		;;
 	none)
 		;;
-	kernel* )
+	kernel* | msvc* )
 		# Restricted further below
 		;;
 	*)
@@ -1785,6 +1786,8 @@ case $kernel-$os in
 		;;
 	managarm-mlibc* | managarm-kernel* )
 		;;
+	windows*-gnu* | windows*-msvc*)
+		;;
 	-dietlibc* | -newlib* | -musl* | -relibc* | -uclibc* | -mlibc* )
 		# These are just libc implementations, not actual OSes, and thus
 		# require a kernel.
@@ -1799,6 +1802,10 @@ case $kernel-$os in
 		echo "Invalid configuration '$1': '$kernel' does not support '$os'." 1>&2
 		exit 1
 		;;
+	*-msvc* )
+		echo "Invalid configuration '$1': '$os' needs 'windows'." 1>&2
+		exit 1
+		;;
 	kfreebsd*-gnu* | kopensolaris*-gnu*)
 		;;
 	vxworks-simlinux | vxworks-simwindows | vxworks-spe)