MavenPackage: allow additional build args (#19676)

lib/spack/docs/build_systems/mavenpackage.rst

@@ -76,6 +76,24 @@ should add:
    depends_on('maven@3.5.4:', type='build')
 
 
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Passing arguments to the build phase
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The default build and install phases should be sufficient to install
+most packages. However, you may want to pass additional flags to
+the build phase. For example:
+
+.. code-block:: python
+
+   def build_args(self):
+       return [
+           '-Pdist,native',
+           '-Dtar',
+           '-Dmaven.javadoc.skip=true'
+       ]
+
+
 ^^^^^^^^^^^^^^^^^^^^^^
 External documentation
 ^^^^^^^^^^^^^^^^^^^^^^