[PyQt] sip changesets 71a8ee38b2c6 & 948e06cb1921 (sip 4.19.1) break QGIS

[Doug Newgard]

QGIS builds fine with sip 4.19, but fails with 4.19.1. I bisected and found
that these two changesets are where things go wrong, it builds fine with
6b23496bd532 and earlier but fails with the following errors with 948e06cb1921
and later.

/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp:5798:7: error: delet
ed function ‘virtual sipQgsFileDownloader::~sipQgsFileDownloader()’
 }
       ^
In file included from /home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/gui/qgsfiledownloader.sip
:33:0:
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/../src/gui/qgsfiledownloader.h:94:5: error: ove
rriding non-deleted function ‘virtual QgsFileDownloader::~QgsFileDownloader()’
     ~QgsFileDownloader();
     ^
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp:5798:7: note: ‘virtu
al sipQgsFileDownloader::~sipQgsFileDownloader()’ is implicitly deleted because the default definiti
on would be ill-formed:
 }
       ^
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp:5798:7: error: ‘virt
ual QgsFileDownloader::~QgsFileDownloader()’ is private within this context
In file included from /home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/gui/qgsfiledownloader.sip
:33:0:
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/../src/gui/qgsfiledownloader.h:94:5: note: decl
ared private here
     ~QgsFileDownloader();
     ^
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp: In constructor ‘sip
QgsFileDownloader::sipQgsFileDownloader(QUrl, QString, bool)’:
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp:5830:122: error: ‘Qg
sFileDownloader::~QgsFileDownloader()’ is private within this context
 bool sipQgsFileDownloader::eventFilter( ::QObject*a0, ::QEvent*a1)

                      ^
In file included from /home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/gui/qgsfiledownloader.sip
:33:0:
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/python/../src/gui/qgsfiledownloader.h:94:5: note: declared private here
     ~QgsFileDownloader();
     ^
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp: In function ‘void release_QgsFileDownloader(void*, int)’:
/home/dnewgard/PKGBUILDs/qgis/src/qgis-2.18.3/build/python/gui/sip_guipart3.cpp:6028:64: error: use of deleted function ‘virtual sipQgsFileDownloader::~sipQgsFileDownloader()’
                 return NULL;
                                                                ^


I know little about sip, is this a regression with sip or something that QGIS
needs to fix? With both changesets talking about fixing regressions, I
wouldn't expect them to break things, so I'm trying here first.

Doug