configure: Pass the right machine types to dlltool for arm and arm64 mingw

These are supported by llvm-dlltool.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -3894,6 +3894,10 @@ case $target_os in
         LIBTARGET=i386
         if enabled x86_64; then
             LIBTARGET="i386:x86-64"
+        elif enabled arm; then
+            LIBTARGET="arm"
+        elif enabled aarch64; then
+            LIBTARGET="arm64"
         fi
         if enabled shared; then
             # Cannot build both shared and static libs when using dllimport.