Fixed compile warnings in posix_logger.h and coding.h

Summary:
Fixed the following compile warnings:

/Users/yhchiang/rocksdb/util/posix_logger.h:32:11: error: unused variable 'kDebugLogChunkSize' [-Werror,-Wunused-const-variable]
const int kDebugLogChunkSize = 128 * 1024;
          ^
/Users/yhchiang/rocksdb/util/coding.h:24:20: error: unused variable 'kMaxVarint32Length' [-Werror,-Wunused-const-variable]
const unsigned int kMaxVarint32Length = 5;
                   ^
2 errors generated.

Test Plan: make clean rocksdb

Reviewers: igor, sdong, anthony, IslamAbdelRahman, rven, kradhakrishnan, adamretter

Reviewed By: adamretter

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D56223

port/win/win_logger.h

@@ -23,8 +23,6 @@ namespace rocksdb {
 
 class Env;
 
-const int kDebugLogChunkSize = 128 * 1024;
-
 class WinLogger : public rocksdb::Logger {
  public:
   WinLogger(uint64_t (*gettid)(), Env* env, HANDLE file,

util/coding.h

@@ -23,8 +23,7 @@
 
 namespace rocksdb {
 
-// The maximum length of a varint in bytes for 32 and 64 bits respectively.
+// The maximum length of a varint in bytes for 64-bit.
-const unsigned int kMaxVarint32Length = 5;
 const unsigned int kMaxVarint64Length = 10;
 
 // Standard Put... routines append to a string

util/posix_logger.h

@@ -30,8 +30,6 @@
 
 namespace rocksdb {
 
-const int kDebugLogChunkSize = 128 * 1024;
-
 class PosixLogger : public Logger {
  private:
   FILE* file_;
@@ -129,6 +127,8 @@ class PosixLogger : public Logger {
       const size_t write_size = p - base;
 
 #ifdef ROCKSDB_FALLOCATE_PRESENT
+      const int kDebugLogChunkSize = 128 * 1024;
+
       // If this write would cross a boundary of kDebugLogChunkSize
       // space, pre-allocate more space to avoid overly large
       // allocations from filesystem allocsize options.