add arch tuple matching for nt32 and nt64 in configure

the nt32 and nt64 archs will be provided by the midipix project for
building musl on top of its posix-like syscall layer for windows. at
present the needed arch files are in a separate repository, but having
the tuple matching in the upstream configure script should make it
possible to overlay the arch files without needing any further
diff --git a/configure b/configure
index 5a92ea0..0955ce6 100755
--- a/configure
+++ b/configure
@@ -302,8 +302,10 @@
 mips64*|powerpc64*) fail "$0: unsupported target \"$target\"" ;;
 arm*) ARCH=arm ;;
 aarch64*) ARCH=aarch64 ;;
+i?86-nt32*) ARCH=nt32 ;;
 i?86*) ARCH=i386 ;;
 x86_64-x32*|x32*|x86_64*x32) ARCH=x32 ;;
+x86_64-nt64*) ARCH=nt64 ;;
 x86_64*) ARCH=x86_64 ;;
 mips*) ARCH=mips ;;
 microblaze*) ARCH=microblaze ;;