Add a target config for MINGW on ARM64

This is necessary to build OpenSSL native on Windows on Arm64 with gcc or clang.
It also works when cross compiling on Linux for aarch64-w64-windows-gnu.

This patch is used since years on MSYS2:
  https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-openssl/001-support-aarch64.patch

Fixes #10533

Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26605)

Configurations/10-main.conf

@@ -1746,6 +1746,18 @@ my %targets = (
         multilib         => "64",
     },
 
+    "mingwarm64" => {
+        inherit_from     => [ "mingw-common" ],
+        cflags           => "",
+        sys_id           => "MINGWARM64",
+        bn_ops           => add("SIXTY_FOUR_BIT"),
+        asm_arch         => 'aarch64',
+        uplink_arch      => 'armv8',
+        perlasm_scheme   => "win64",
+        shared_rcflag    => "",
+        multilib         => "-arm64",
+    },
+
 #### UEFI
     "UEFI" => {
         inherit_from     => [ "BASE_unix" ],