Have configure.py modify internal variables depending on the --qml-plugindir
configure option.
diff -u PyQt-gpl-5.4.alt/configure.py PyQt-gpl-5.4/configure.py
--- PyQt-gpl-5.4.alt/configure.py	2015-01-25 17:27:50.000000000 +0100
+++ PyQt-gpl-5.4/configure.py	2015-01-25 17:56:41.000000000 +0100
@@ -904,6 +904,9 @@
         if opts.pyuicinterpreter is not None:
             self.pyuic_interpreter = opts.pyuicinterpreter
 
+        if opts.qmlplugindir is not None:
+            self.qml_plugin_dir = opts.qmlplugindir
+
         if opts.qsciapidir is not None:
             self.qsci_api_dir = opts.qsciapidir
 
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<tr><td><span title='2017-03-30 22:59:53 +0200'>2017-03-30</span></td><td><a href='/guix/commit/gnu/packages/gperf.scm?id=84157bb8bf2c610584e0836047da4c710f8eaf76'>Merge branch 'master' into core-updates</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2017-03-30 01:30:16 +0200'>2017-03-30</span></td><td><a href='/guix/commit/gnu/packages/gperf.scm?id=6fd52309b8f52c9bb59fccffac53e029ce94b698'>gnu: Use HTTPS for almost all gnu.org HOME-PAGEs.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-03-19 23:42:57 +0100'>2017-03-19</span></td><td><a href='/guix/commit/gnu/packages/gperf.scm?id=4ed06287376bc1632c6bca4a395795bc8cc1b874'>gnu: elogind: Build with gperf 3.0.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-02-17 07:14:40 +0100'>2017-02-17</span></td><td><a href='/guix/commit/gnu/packages/gperf.scm?id=c5481600bbc27111f154e22c37ebc0824a575b26'>gnu: gperf: Update to 3.1</a><span class='msg-avail'>...</span></td><td>John Darrington</td></tr>