Fix compilation issues on GCC/CLANG
 Address Windows Release test build issues due to Sync

  Summary. A change https://reviews.facebook.net/differential/diff/224721/
  Has attempted to move common functionality out of platform dependent
  code to a new facility called file_reader_writer.
  This includes:
  - perf counters
  - Buffering
  - RateLimiting

  However, the change did not attempt to refactor Windows code.
  To mitigate, we introduce new quering interfaces such as UseOSBuffer(),
  GetRequiredBufferAlignment() and ReaderWriterForward()
  for pure forwarding where required.
  Introduce WritableFile got a new method Truncate(). This is to communicate
  to the file as to how much data it has on close.
   - When space is pre-allocated on Linux it is filled with zeros implicitly,
    no such thing exist on Windows so we must truncate file on close.
   - When operating in unbuffered mode the last page is filled with zeros but we still want to truncate.

   Previously, Close() would take care of it but now buffer management is shifted to the wrappers and the file has
   no idea about the file true size.

   This means that Close() on the wrapper level must always include
   Truncate() as well as wrapper __dtor should call Close() and
   against double Close().
   Move buffered/unbuffered write logic to the wrapper.
   Utilize Aligned buffer class.
   Adjust tests and implement Truncate() where necessary.
   Come up with reasonable defaults for new virtual interfaces.
   Forward calls for RandomAccessReadAhead class to avoid double
   buffering and locking (double locking in unbuffered mode on WIndows).

  Previous change for the function
  https://github.com/facebook/rocksdb/commit/555ca3e7b7f06bd01dfd5e04dbb2cef5360f7917#diff-bdc04e0404c2db4fd3ac5118a63eaa4a
  made use of the QueryPerformanceCounter to return microseconds values that do not repeat
  as std::chrono::system_clock returned values that made auto_roll_logger_test fail.

 The interface documentation does not state that we need to return
 system time describing the return value as a number of microsecs since some
 moment in time. However, because on Linux it is implemented using gettimeofday
 various pieces of code (such as GenericRateLimiter) took advantage of that
 and make use of NowMicros() as a system timestamp. Thus the previous change
 broke rate_limiter_test on Windows.

 In addition, the interface name NowMicros() suggests that it is actually
 a timestamp so people use it as such.

 This change makes use of the new system call on Windows that returns
 system time with required precision. This change preserves the fix
 for  auto_roll_logger_test and fixes rate_limiter_test.

 Note that DBTest.RateLimitingTest still fails due to a separately reported issue.

Summary: RandomRWFile is not used anywhere in out code base, this patch remove RandomRWFile

Test Plan:
make check -j64
USE_CLANG=1 make all -j64
OPT=-DROCKSDB_LITE make release -j64

Reviewers: sdong, yhchiang, anthony, kradhakrishnan, rven, igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D44091

  * std::chrono does not provide enough granularity for microsecs and periodically emits
    duplicates
  * the bug is manifested in log rotation logic where we get duplicate
   log file names and loose previous log content
  * msvc does not imlement COW on std::strings adjusted the test to use
    refs in the loops as auto does not retain ref info
  * adjust auto_log rotation test with Windows specific command to remove
    a folder. The test previously worked because we have unix utils installed
    in house but this may not be the case for everyone.

Summary: Add new CheckFileExists method.  Considered changing the FileExists api but didn't want to break anyone's builds.

Test Plan: unit tests

Reviewers: yhchiang, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D42003

Move rate_limiter, write buffering, most perf context instrumentation and most random kill out of Env

Summary: We want to keep Env a think layer for better portability. Less platform dependent codes should be moved out of Env. In this patch, I create a wrapper of file readers and writers, and put rate limiting, write buffering, as well as most perf context instrumentation and random kill out of Env. It will make it easier to maintain multiple Env in the future.

Test Plan: Run all existing unit tests.

Reviewers: anthony, kradhakrishnan, IslamAbdelRahman, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D42321

Summary: This helps Windows port to format their changes, as discussed. Might have formatted some other codes too becasue last 10 commits include more.

Test Plan: Build it.

Reviewers: anthony, IslamAbdelRahman, kradhakrishnan, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D41961

     1) Crash in env_win.cc that prevented db_test run to completion and some new tests
     2) Fix new corruption tests in DBTest by allowing a shared trunction of files. Note that this is generally needed ONLY for tests.
     3) Close database so WAL is closed prior to inducing corruption similar to what we did within Corruption tests.

 Summary: Make RocksDb build and run on Windows to be functionally
 complete and performant. All existing test cases run with no
 regressions. Performance numbers are in the pull-request.

 Test plan: make all of the existing unit tests pass, obtain perf numbers.

 Co-authored-by: Praveen Rao praveensinghrao@outlook.com
 Co-authored-by: Sherlock Huang baihan.huang@gmail.com
 Co-authored-by: Alex Zinoviev alexander.zinoviev@me.com
 Co-authored-by: Dmitri Smirnov dmitrism@microsoft.com