make PRS and BC0 compression deterministic across environments

src/Compression.hh

@@ -4,6 +4,7 @@
 
 #include <string>
 #include <functional>
+#include <set>
 
 #include "Text.hh"
 
@@ -50,7 +51,7 @@ private:
   parray<uint8_t, 0x100> forward_log;
   size_t compression_offset;
   parray<uint8_t, 0x2000> reverse_log;
-  std::vector<std::unordered_set<size_t>> reverse_log_index;
+  std::vector<std::set<size_t>> reverse_log_index;
 
   StringWriter output;
 };