Check for symbol available on both Ubuntu 14.04 and 16.04 lz4 packages
Check for symbol available on both Ubuntu 14.04 and 16.04 lz4 packages

Summary:
I had tried to check for `LZ4_freeStream`, but this symbol is not available in
earlier versions of lz4.  The symbol `LZ4_decompress_safe` is available in
lz4 packages on both 14.04 and 16.04.

Reviewed By: glamtechie

Differential Revision: D5309052

fbshipit-source-id: 8795634e1fca8b26e2d9bdee2992c43ab082fffa

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter