Update lz4 to a version compatible with gcc 4.9+

Not 100% sure of the reason but lz4 gets mis-optimized (or "has UB"
depending on who you ask) in the version that we're using, so update
to a version that has a fix.

lz4 @ d86dc916

-Subproject commit 160661c7a4cbf805f4af74d2e3932a17a66e6ce7
+Subproject commit d86dc916771c126afb797637dda9f6421c0cb998