depends: Upgrade Qt to 5.9.6

Summary:

• Ugrade Qt depends to Qt5.9.4

Depends can now be built with Qt5.9.4 , which is Qt's new long term
support version.

• Fix depends Qt5.9.4 mac build

Apply patch from QTBUG-67286

• Upgrade Qt depends to 5.9.6

This is a backport of Core's PR12971

Depends on D1819

Test Plan:

make -C ../depends build-all

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1820