set snappy compression only when supported (#4325)

Summary:
Right now `OptimizeLevelStyleCompaction` may set compression type to Snappy even when Snappy is not supported, this may cause errors like "no snappy compression support"
Fixes https://github.com/facebook/rocksdb/issues/4283
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4325

Differential Revision: D15125542

Pulled By: miasantreble

fbshipit-source-id: 70890b73ababe16752721555dbd290633c2aafac

options/options.cc

@@ -548,7 +548,10 @@ ColumnFamilyOptions* ColumnFamilyOptions::OptimizeLevelStyleCompaction(
     if (i < 2) {
       compression_per_level[i] = kNoCompression;
     } else {
-      compression_per_level[i] = kSnappyCompression;
+      compression_per_level[i] =
+          LZ4_Supported()
+              ? kLZ4Compression
+              : (Snappy_Supported() ? kSnappyCompression : kNoCompression);
     }
   }
   return this;