Win32: added detection of ARM64 target.

This extends the target selection implemented in dad6ec3aa6 to support
Windows ARM64 platforms.  OpenSSL support for VC-WIN64-ARM target first
appeared in 1.1.1 and is present in all currently supported (3.x)
branches.

As a side effect, ARM64 Windows builds will get 16-byte alignment along
with the rest of non-x86 platforms.  This is safe, as malloc on 64-bit
Windows guarantees the fundamental alignment of allocations, 16 bytes.

auto/cc/msvc

@@ -26,6 +26,10 @@ ngx_msvc_ver=`echo $NGX_MSVC_VER | sed -e 's/^\([0-9]*\).*/\1/'`
 
 case "$NGX_MSVC_VER" in
 
+    *ARM64)
+        NGX_MACHINE=arm64
+    ;;
+
     *x64)
         NGX_MACHINE=amd64
     ;;

auto/lib/openssl/make

@@ -13,6 +13,10 @@ case "$CC" in
                 OPENSSL_TARGET=VC-WIN64A
             ;;
 
+            arm64)
+                OPENSSL_TARGET=VC-WIN64-ARM
+            ;;
+
             *)
                 OPENSSL_TARGET=VC-WIN32
             ;;