Revert "Set the correct target for mingw64 dlltool"

Revert due to dlltool/lib revert
This reverts commit 417516f63f8a9ee214ee9fa6fcb483962ea0f096.

configure

@@ -2429,7 +2429,7 @@ case $target_os in
         LIBTARGET=i386
         if enabled x86_64; then
             enable malloc_aligned
-            LIBTARGET="i386:x86-64"
+            LIBTARGET=x64
         elif enabled arm; then
             LIBTARGET=arm-wince
         fi