Finddouble-conversion: add imported targets

CMake/Finddouble-conversion.cmake

-find_path(DOUBLE-CONVERSION_INCLUDE_DIR
+find_path(double-conversion_INCLUDE_DIR
   NAMES
     double-conversion.h
   PATH_SUFFIXES
-    double-conversion)
+    double-conversion
+  DOC "double-conversion include directory")
+mark_as_advanced(double-conversion_INCLUDE_DIR)
 
-find_library(DOUBLE-CONVERSION_LIBRARY
+find_library(double-conversion_LIBRARY
   NAMES
     double-conversion
-    )
-
-set(DOUBLE-CONVERSION_LIBRARIES "${DOUBLE-CONVERSION_LIBRARY}")
-
-add_library(double-conversion::double-conversion UNKNOWN IMPORTED)
-set_target_properties(double-conversion::double-conversion
-  PROPERTIES
-  IMPORTED_LOCATION ${DOUBLE-CONVERSION_LIBRARY}
-  INTERFACE_INCLUDE_DIRECTORIES ${DOUBLE-CONVERSION_INCLUDE_DIR})
+  DOC "double-conversion library")
+mark_as_advanced(double-conversion_LIBRARY)
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(double-conversion
-  DOUBLE-CONVERSION_LIBRARIES
-  DOUBLE-CONVERSION_INCLUDE_DIR
-)
+  REQUIRED_VARS double-conversion_LIBRARY double-conversion_INCLUDE_DIR)
+
+if (double-conversion_FOUND)
+  set(double-conversion_INCLUDE_DIRS "${double-conversion_INCLUDE_DIR}")
+  set(double-conversion_LIBRARIES "${double-conversion_LIBRARY}")
 
-mark_as_advanced(DOUBLE-CONVERSION_LIBRARY DOUBLE-CONVERSION_INCLUDE_DIR)
+  if (NOT TARGET double-conversion::double-conversion)
+    add_library(double-conversion::double-conversion UNKNOWN IMPORTED)
+    set_target_properties(double-conversion::double-conversion PROPERTIES
+      IMPORTED_LOCATION "${double-conversion_LIBRARY}"
+      INTERFACE_INCLUDE_DIRECTORIES "${double-conversion_INCLUDE_DIR}")
+  endif ()
+endif ()