maintainer-feedback requested: [Bug 231584] devel/qt5-buildtools: fix build on architectures using base GCC

[bugzilla-noreply at freebsd.org]

Bugzilla Automation <bugzilla at FreeBSD.org> has asked kde at FreeBSD.org for
maintainer-feedback:
Bug 231584: devel/qt5-buildtools: fix build on architectures using base GCC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231584



--- Description ---
Similarly to devel/qt5-qmake, this patch redefines mkspecs to allow building
with gcc7 port when base GCC is present.

It also adds USES=compiler:c++17-lang, since -std=c++1z is used during
compilation.

Tested on powerpc64 and on amd64 with clang.