Remove -Wno-unused-const-variable

Makefile

@@ -44,7 +44,7 @@ else
 	PLATFORM_CCFLAGS += $(JEMALLOC_INCLUDE) -DHAVE_JEMALLOC
 endif
 
-WARNING_FLAGS = -Wall -Werror -Wno-sign-compare -Wno-unused-const-variable
+WARNING_FLAGS = -Wall -Werror -Wno-sign-compare
 CFLAGS += $(WARNING_FLAGS) -I. -I./include $(PLATFORM_CCFLAGS) $(OPT)
 CXXFLAGS += $(WARNING_FLAGS) -I. -I./include $(PLATFORM_CXXFLAGS) $(OPT) -Woverloaded-virtual
 

include/rocksdb/perf_context.h

@@ -64,7 +64,7 @@ struct PerfContext {
   uint64_t write_memtable_time;
 };
 
-#if defined(OS_MACOSX)
+#if defined(IOS_CROSS_COMPILE)
 extern PerfContext perf_context;
 #else
 extern __thread PerfContext perf_context;

table/block_based_table_reader.cc

@@ -45,7 +45,9 @@ namespace {
 // The longest the prefix of the cache key used to identify blocks can be.
 // We are using the fact that we know for Posix files the unique ID is three
 // varints.
-const size_t kMaxCacheKeyPrefixSize = kMaxVarint64Length*3+1;
+// For some reason, compiling for iOS complains that this variable is unused
+const size_t kMaxCacheKeyPrefixSize __attribute__((unused)) =
+    kMaxVarint64Length * 3 + 1;
 
 // Read the block identified by "handle" from "file".
 // The only relevant option is options.verify_checksums for now.