package/qt5: bump minimum gcc requirement to 5.0

package/qt5: bump minimum gcc requirement to 5.0

As a side effect of avoiding gcc bug 57694 ([1]) through commit
'GCC: revoke constexpr before 5.0' ([2]) for qtbase the minimum
gcc requirement was lifted to 5.0 ([3], [4]), so bump the
buildroot determined one too.

Adjust the two packages (pinentry, wireshark) which are brave enough
to do a 'select BR2_PACKAGE_QT5' accordingly.

Fixes:
  http://autobuild.buildroot.net/results/74f5249d1ee14c1269685af53a65055da7dc2ee6

  ../../include/QtCore/../../src/corelib/thread/qbasicatomic.h:61:4: error: #error "Qt requires C++11 support"
   #  error "Qt requires C++11 support"

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57694
[2] https://code.qt.io/cgit/qt/qtbase.git/commit/?id=c61cedcc5475a77fb94ed12788f61039835f8079
[3] https://codereview.qt-project.org/c/qt/qtbase/+/285582
[4] https://bugreports.qt.io/browse/QTBUG-81761

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>