cmake: detect lz4 version, require >= 1.6

cmake/FindLZ4.cmake

 find_path(LZ4_INCLUDE_DIRS NAMES lz4.h)
 find_library(LZ4_LIBRARIES NAMES lz4)
 
+if(LZ4_INCLUDE_DIRS AND EXISTS "${LZ4_INCLUDE_DIRS}/lz4.h")
+  file(STRINGS "${LZ4_INCLUDE_DIRS}/lz4.h" LZ4_H REGEX "^#define LZ4_VERSION_[MR]")
+  string(REGEX REPLACE "LZ4_VERSION" "" LZ4_H "${LZ4_H}")
+  string(REGEX MATCHALL "[0-9]+" LZ4_H "${LZ4_H}")
+  string(REGEX REPLACE ";" "." LZ4_VERSION_STRING "${LZ4_H}")
+endif()
+
 include(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(
-    LZ4 DEFAULT_MSG
-    LZ4_LIBRARIES LZ4_INCLUDE_DIRS)
+    LZ4
+    REQUIRED_VARS LZ4_LIBRARIES LZ4_INCLUDE_DIRS
+    VERSION_VAR LZ4_VERSION_STRING)
 
 mark_as_advanced(LZ4_INCLUDE_DIRS LZ4_LIBRARIES)

plugin/provider_lz4/CMakeLists.txt

-FIND_PACKAGE(LZ4)
+FIND_PACKAGE(LZ4 1.6)
 
 IF (LZ4_FOUND)
   GET_PROPERTY(dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES)