missing emhash/bench/martin_bench.cpp

[renau]

The cmake points to a file that does not exit in the repo.

mkdir build
cd build
cmake ../
...
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Configuring done (3.0s)
CMake Error at CMakeLists.txt:37 (add_executable):
  Cannot find source file:

   XXX/emhash/bench/martin_bench.cpp

[ktprime]

use makefile to compile benchmark code. ( CMakeLists.txt is not updated)

[ktprime]

refer to https://github.com/ktprime/emhash/blob/master/bench/README.md to build benchmark code