FindLZ4: make imported targets

CMake/FindLZ4.cmake

+find_path(LZ4_INCLUDE_DIR
+  NAMES lz4.h
+  DOC "lz4 include directory")
+mark_as_advanced(LZ4_INCLUDE_DIR)
+find_library(LZ4_LIBRARY
+  NAMES lz4
+  DOC "lz4 library")
+mark_as_advanced(LZ4_LIBRARY)
 
-find_library(LZ4_LIBRARIES NAMES lz4)
-find_path(LZ4_INCLUDE_DIRS NAMES lz4.h)
+if (LZ4_INCLUDE_DIR)
+  file(STRINGS "${LZ4_INCLUDE_DIR}/lz4.h" _lz4_version_lines
+    REGEX "#define[ \t]+LZ4_VERSION_(MAJOR|MINOR|RELEASE)")
+  string(REGEX REPLACE ".*LZ4_VERSION_MAJOR *\([0-9]*\).*" "\\1" _lz4_version_major "${_lz4_version_lines}")
+  string(REGEX REPLACE ".*LZ4_VERSION_MINOR *\([0-9]*\).*" "\\1" _lz4_version_minor "${_lz4_version_lines}")
+  string(REGEX REPLACE ".*LZ4_VERSION_RELEASE *\([0-9]*\).*" "\\1" _lz4_version_release "${_lz4_version_lines}")
+  set(LZ4_VERSION "${_lz4_version_major}.${_lz4_version_minor}.${_lz4_version_release}")
+  unset(_lz4_version_major)
+  unset(_lz4_version_minor)
+  unset(_lz4_version_release)
+  unset(_lz4_version_lines)
+endif ()
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(LZ4
-  DEFAULT_MSG
-  LZ4_LIBRARIES
-  LZ4_INCLUDE_DIRS)
+  REQUIRED_VARS LZ4_LIBRARY LZ4_INCLUDE_DIR
+  VERSION_VAR LZ4_VERSION)
+
+if (LZ4_FOUND)
+  set(LZ4_INCLUDE_DIRS "${LZ4_INCLUDE_DIR}")
+  set(LZ4_LIBRARIES "${LZ4_LIBRARY}")
+
+  if (NOT TARGET LZ4::LZ4)
+    add_library(LZ4::LZ4 UNKNOWN IMPORTED)
+    set_target_properties(LZ4::LZ4 PROPERTIES
+      IMPORTED_LOCATION "${LZ4_LIBRARY}"
+      INTERFACE_INCLUDE_DIRECTORIES "${LZ4_INCLUDE_DIR}")
+  endif ()
+endif ()