The build.xml file is in the wrong location. It should be in the base directory of the project, not in the src directory.
The error that you are getting says that it expected to find a src subdirectory under the directory that contains build.xml. And since build.xml is at AntWebProject/src, then it expects to find AntWebProject/src/src. In general, all relative paths specified in build.xml are relative to the directory containing build.xml, regardless of the directory from which you issued the ant command.