Adding zstd to build

Summary:
This is in order for us to share compression ops to oss.
Closes https://github.com/caffe2/caffe2/pull/1463

Reviewed By: hlu1

Differential Revision: D6319101

Pulled By: Yangqing

fbshipit-source-id: 16c94e71fc3efe256054a648170aaf7702e5bcfe

.gitmodules

@@ -49,3 +49,6 @@
 [submodule "third_party/aten"]
 	path = third_party/aten
 	url = https://github.com/zdevito/aten
+[submodule "third_party/zstd"]
+	path = third_party/zstd
+	url = https://github.com/facebook/zstd.git

CMakeLists.txt

@@ -41,6 +41,7 @@ option(USE_ROCKSDB "Use RocksDB" ON)
 option(USE_SNPE "Use Qualcomm's SNPE library" OFF)
 option(USE_THREADS "Use Threads" ON)
 option(USE_ZMQ "Use ZMQ" OFF)
+option(USE_ZSTD "Use ZSTD" OFF)
 
 
 # ---[ CMake scripts + modules

cmake/Dependencies.cmake

@@ -36,7 +36,6 @@ else()
 endif()
 
 
-
 # ---[ BLAS
 set(BLAS "Eigen" CACHE STRING "Selected BLAS library")
 set_property(CACHE BLAS PROPERTY STRINGS "Eigen;ATLAS;OpenBLAS;MKL;vecLib")
@@ -473,3 +472,7 @@ if (USE_ATEN)
   caffe2_include_directories(${PROJECT_SOURCE_DIR}/third_party/aten/src)
   caffe2_include_directories(${PROJECT_BINARY_DIR}/caffe2/contrib/aten)
 endif()
+
+if (USE_ZSTD)
+  add_subdirectory(${PROJECT_SOURCE_DIR}/third_party/zstd/build/cmake)
+endif()