Add FindLZ4 module

Summary:
Add a CMake find_package script for LZ4

simpkins
Closes https://github.com/facebook/folly/pull/778

Reviewed By: simpkins

Differential Revision: D7064988

Pulled By: yfeldblum

fbshipit-source-id: 60596ead4b4fd38474dab4c33d4c3fbb0f37549c

CMake/FindLZ4.cmake

+# Finds liblz4.
+#
+# This module defines:
+# LZ4_FOUND
+# LZ4_INCLUDE_DIR
+# LZ4_LIBRARY
+#
+
+find_path(LZ4_INCLUDE_DIR NAMES lz4.h)
+find_library(LZ4_LIBRARY NAMES lz4)
+
+include(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(
+    LZ4 DEFAULT_MSG
+    LZ4_LIBRARY LZ4_INCLUDE_DIR
+)
+
+if (LZ4_FOUND)
+    message(STATUS "Found LZ4: ${LZ4_LIBRARY}")
+endif()
+
+mark_as_advanced(LZ4_INCLUDE_DIR LZ4_LIBRARY)

CMake/folly-deps.cmake

@@ -98,6 +98,13 @@ if (LIBLZMA_FOUND)
   list(APPEND FOLLY_LINK_LIBRARIES ${LIBLZMA_LIBRARIES})
 endif()
 
+find_package(lz4 MODULE)
+set(FOLLY_HAVE_LIBLZ4 ${LZ4_FOUND})
+if (LZ4_FOUND)
+  list(APPEND FOLLY_INCLUDE_DIRECTORIES ${LZ4_INCLUDE_DIR})
+  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)
@@ -108,10 +115,6 @@ CHECK_INCLUDE_FILE_CXX(snappy.h FOLLY_HAVE_LIBSNAPPY)
 if (FOLLY_HAVE_LIBSNAPPY)
   list(APPEND FOLLY_LINK_LIBRARIES snappy)
 endif()
-CHECK_INCLUDE_FILE_CXX(lz4.h FOLLY_HAVE_LIBLZ4)
-if (FOLLY_HAVE_LIBLZ4)
-  list(APPEND FOLLY_LINK_LIBRARIES lz4)
-endif()
 
 find_package(LibDwarf)
 list(APPEND FOLLY_LINK_LIBRARIES ${LIBDWARF_LIBRARIES})