Fix a bunch of mac compilation issues in performance branch

table/plain_table_builder.cc

@@ -23,8 +23,7 @@ namespace rocksdb {
 PlainTableBuilder::PlainTableBuilder(const Options& options,
                                      WritableFile* file,
                                      int user_key_size, int key_prefix_len) :
-    options_(options), file_(file), user_key_size_(user_key_size),
-    key_prefix_len_(key_prefix_len) {
+    options_(options), file_(file), user_key_size_(user_key_size) {
   std::string version;
   PutFixed32(&version, 1 | 0x80000000);
   file_->Append(Slice(version));

table/plain_table_builder.h

@@ -75,7 +75,6 @@ private:
   uint64_t num_entries_ = 0;
 
   const size_t user_key_size_;
-  const size_t key_prefix_len_;
   bool closed_ = false;  // Either Finish() or Abandon() has been called.
 
   int GetInternalKeyLength() {

table/plain_table_reader.cc

@@ -40,7 +40,8 @@ public:
 
 class slice_comparator {
 public:
-  bool operator()(rocksdb::Slice const& s1, rocksdb::Slice const& s2) {
+  bool operator()(rocksdb::Slice const& s1,
+                  rocksdb::Slice const& s2) const {
     return s1.compare(s2) < 0;
   }
 };

util/env_posix.cc

@@ -1404,11 +1404,13 @@ class PosixEnv : public Env {
                 (unsigned long)t);
 
         // Set the thread name to aid debugging
-#if defined(_GNU_SOURCE) && defined(__GLIBC_PREREQ) && (__GLIBC_PREREQ(2, 12))
+#if defined(_GNU_SOURCE) && defined(__GLIBC_PREREQ)
+#if __GLIBC_PREREQ(2, 12)
         char name_buf[16];
         snprintf(name_buf, sizeof name_buf, "rocksdb:bg%zu", bgthreads_.size());
         name_buf[sizeof name_buf - 1] = '\0';
         pthread_setname_np(t, name_buf);
+#endif
 #endif
 
         bgthreads_.push_back(t);