Enable creation of microsoft-style import libraries on arm.

Patch by Martin Storsjo <martin at martin dot st>

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@19426 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -1699,6 +1699,8 @@ case $target_os in
         if enabled x86_64; then
             disable need_memalign
             LIBTARGET=x64
+        elif enabled arm; then
+            LIBTARGET=arm
         fi
         shlibdir_default="$bindir_default"
         disable ffserver