Update cmake script to avoid fatal error when GLEW and GLFWH are missing.

Former-commit-id: 758f197f1c01b4667c30968de6a8e4142e52399d

tutorial/cmake/FindGLEW.cmake

@@ -32,7 +32,7 @@ if(GLEW_FOUND)
   set(GLEW_SOURCES ${GLEW_INCLUDE_DIR}/../src/glew.c)
   message(STATUS "Found GLEW: ${GLEW_INCLUDE_DIR}")
 else(GLEW_FOUND)
-  message(FATAL_ERROR "could NOT find glew")
+  message("could NOT find glew")
 endif(GLEW_FOUND)
 
 MARK_AS_ADVANCED(GLEW_INCLUDE_DIR)

tutorial/cmake/FindGLFWH.cmake

@@ -37,7 +37,7 @@ if(GLFW_FOUND)
   message(STATUS "Found GLFW: ${GLFW_INCLUDE_DIR} -- HEADERS ONLY")
 else(GLFW_FOUND)
   if (NOT GLFW_FIND_QUIETLY)
-    message(FATAL_ERROR "could NOT find GLFW")
+    message("could NOT find GLFW")
   endif (NOT GLFW_FIND_QUIETLY)
 endif(GLFW_FOUND)