depends: Fix Qt build with XCode 9.3 #12946

Building Qt with Xcode 9.3 is currently broken with:

compiling kernel/qmacgesturerecognizer.cpp
fontdatabases/mac/qfontengine_coretext.mm:775:20: error: qualified reference to 'QFixed' is a constructor name rather than a type in this context
    return QFixed::QFixed(int(CTFontGetUnitsPerEm(ctfont)));
                   ^
compiling .moc/moc_qfbscreen_p.cpp
1 error generated.
make[2]: *** [.obj/qfontengine_coretext.o] Error 1
make[2]: *** Waiting for unfinished jobs....

This patch should fix that, and will hopefully be the last time we have to patch Qt 5.7.

I've only made minor adjustments from the original patch, so that it will apply, although still not completely cleanly. We can cleanup if required.

Concept ACK

I was initially confused by the PR description into thinking bitcoin-qt didn't build, but you're referring to QT itself via the depends system.

I didn't try before updating the command line tools in Xcode 9.3, but indeed building QT on macOS 10.13.4 is broken for me:

cd depends
make
...
compiling util/qundoview.cpp
rm -f ../../lib/libQt5Widgets.a
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar cq ../../lib/libQt5Widgets.a .obj/qaction.o .obj/qactiongroup.o .obj/qapplication.o
...
.obj/moc_qmacstyle_mac_p.o .obj/moc_qmacnativewidget_mac.o .obj/moc_qmaccocoaviewcontainer_mac.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: ../../lib/libQt5Widgets.a(qstylepainter.o) has no symbols
...
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: file: ../../lib/libQt5Widgets.a(qscroller_mac.o) has no symbols
make: *** [/Volumes/SSD/src/bitcoin/depends/work/build/x86_64-apple-darwin17.5.0/qt/5.7.1-78660355bf0/qtbase/.stamp_built] Error 2

This PR fixes it for me.

utACK 5b4fc3eca429456628a5db4e4090da294eb1eba1