tilepro: work around module link error with gcc 4.7

commit 3cb3f839 upstream.

gcc 4.7.x is emitting calls to __ffsdi2 where previously
it used to inline the appropriate ctz instructions.
While this needs to be fixed in gcc, it's also easy to avoid
having it cause build failures when building with those
compilers by exporting __ffsdi2 to modules.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/tile/lib/exports.c

@@ -90,4 +90,6 @@ uint64_t __ashrdi3(uint64_t, unsigned int);
 EXPORT_SYMBOL(__ashrdi3);
 uint64_t __ashldi3(uint64_t, unsigned int);
 EXPORT_SYMBOL(__ashldi3);
+int __ffsdi2(uint64_t);
+EXPORT_SYMBOL(__ffsdi2);
 #endif