Add language requirements to CMakeLists.txt

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 2.8)
 
-project(HDF4CPP)
+project(HDF4CPP LANGUAGES CXX)
 
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 
@@ -103,4 +103,4 @@ add_subdirectory(examples)
 install(TARGETS hdf4cpp DESTINATION lib)
 install(FILES ${HEADERS}
         DESTINATION "include/hdf4cpp"
-        )
+        )