ARM: enable PIC for shared libs

Recent versions of gcc generate movw/movt pairs, and the linkers fail
to handle the associated relocations properly.  Those responsible at
Codesourcery have refused to consider fixing this.  Blame them for
making shared libraries slower than they need to be.

Originally committed as revision 20203 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1758,6 +1758,7 @@ case "$arch" in
     ;;
     arm|armv[4567]*l)
         arch="arm"
+        spic=$shared
     ;;
     avr32)
     ;;