update(applications):添加对mavlink相关文件的索引

applications/SConscript

@@ -3,7 +3,11 @@ import os
 
 cwd = GetCurrentDir()
 src = Glob('*.c')
-CPPPATH = [cwd]
+
+project_root = os.path.abspath(os.path.join(cwd, '..'))
+mavlink_path = os.path.join(project_root, 'lib', 'mavlink', 'v2.0')
+
+CPPPATH = [cwd, mavlink_path]
 
 group = DefineGroup('Applications', src, depend = [''], CPPPATH = CPPPATH)