Use python extend_path as pyqt sip fix (#15297)

* try extend path to solve PyQt5.sip not found issue

* disable private sip installation in sippackage class

* undo manual PyQt5 dir creation in py-sip site-packages dir

* fix typo

* fix typo

* also apply fix to PyQt4

* tidy up

* flake8 and tidy up

* tidy and undo hardcoding of python_include_dir

* replace hardcoded python inc dir

* fix minor issues

* rethink include dir variable name

* improve style

* add new versions

* implement new sip setup to qsci installation

* set sip-incdir correctly for the new setup

* setup extend_path thing before qsci python bindings

* take care of conflict

* flake8

* also extend for PyQt4

* improve style

* improve style

* SipPackage build sys should depend on py-sip

* consolidate extend_path fixes into SipPackage

* fix typo

* fix bugs

* flake8

* revert sip doc to pre-resource setup

* import os module

* flake8

Co-authored-by: Sinan81 <sbulut@3vgeomatics.com>

lib/spack/docs/build_systems/sippackage.rst

@@ -51,10 +51,8 @@ Build system dependencies
 ``SIPPackage`` requires several dependencies. Python is needed to run
 the ``configure.py`` build script, and to run the resulting Python
 libraries. Qt is needed to provide the ``qmake`` command. SIP is also
-needed to build the package. SIP is an unusual dependency in that it
-must be installed in the same installation directory as the package,
-so instead of a ``depends_on``, we use a ``resource``. All of these
-dependencies are automatically added via the base class
+needed to build the package. All of these dependencies are automatically
+added via the base class
 
 .. code-block:: python
 
@@ -62,11 +60,7 @@ dependencies are automatically added via the base class
 
    depends_on('qt', type='build')
 
-   resource(name='sip',
-            url='https://www.riverbankcomputing.com/static/Downloads/sip/4.19.18/sip-4.19.18.tar.gz',
-            sha256='c0bd863800ed9b15dcad477c4017cdb73fa805c25908b0240564add74d697e1e',
-            destination='.')
-
+   depends_on('py-sip', type='build')
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Passing arguments to ``configure.py``