replace make serve with nominatim serve command

With the website directory now tied to the project directory instead
of the build directory, it is no longer possible to use make for
running the web server.

nominatim/tools/exec_utils.py

@@ -89,6 +89,13 @@ def run_api_script(endpoint, project_dir, extra_env=None, phpcgi_bin=None,
     return 0
 
 
+def run_php_server(server_address, base_dir):
+    """ Run the built-in server from the given directory.
+    """
+    subprocess.run(['/usr/bin/env', 'php', '-S', server_address],
+                   cwd=str(base_dir), check=True)
+
+
 def run_osm2pgsql(options):
     """ Run osm2pgsql with the given options.
     """