Add find module for zstd

Summary:
Adds a find_package module for Zstd.
Closes https://github.com/facebook/folly/pull/785

Reviewed By: pixelb

Differential Revision: D7080036

Pulled By: yfeldblum

fbshipit-source-id: 018ff087df725de5344a245dea64ce1b813f6938

CMake/FindZstd.cmake

+#
+# - Try to find Facebook zstd library
+# This will define
+# ZSTD_FOUND
+# ZSTD_INCLUDE_DIR
+# ZSTD_LIBRARY
+#
+
+find_path(ZSTD_INCLUDE_DIR NAMES zstd.h)
+find_library(ZSTD_LIBRARY NAMES zstd)
+
+include(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(
+    ZSTD DEFAULT_MSG
+    ZSTD_LIBRARY ZSTD_INCLUDE_DIR
+)
+
+if (ZSTD_FOUND)
+    message(STATUS "Found Zstd: ${ZSTD_LIBRARY}")
+endif()
+
+mark_as_advanced(ZSTD_INCLUDE_DIR ZSTD_LIBRARY)

CMake/folly-deps.cmake

@@ -105,12 +105,13 @@ if (LZ4_FOUND)
   list(APPEND FOLLY_LINK_LIBRARIES ${LZ4_LIBRARY})
 endif()
 
-# TODO: We should ideally build FindXXX modules for the following libraries,
-# rather than the simple checks we currently have here.
-CHECK_INCLUDE_FILE_CXX(zstd.h FOLLY_HAVE_LIBZSTD)
-if (FOLLY_HAVE_LIBZSTD)
-  list(APPEND FOLLY_LINK_LIBRARIES zstd)
+find_package(Zstd MODULE)
+set(FOLLY_HAVE_LIBZSTD ${ZSTD_FOUND})
+if(ZSTD_FOUND)
+  list(APPEND FOLLY_INCLUDE_DIRECTORIES ${ZSTD_INCLUDE_DIR})
+  list(APPEND FOLLY_LINK_LIBRARIES ${ZSTD_LIBRARY})
 endif()
+
 CHECK_INCLUDE_FILE_CXX(snappy.h FOLLY_HAVE_LIBSNAPPY)
 if (FOLLY_HAVE_LIBSNAPPY)
   list(APPEND FOLLY_LINK_LIBRARIES snappy)