qBittorrent: use macports-libcxx

[kencu]

closes: https://trac.macports.org/ticket/62441

Description

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.10.5 14F2511
Xcode 7.2.1 7C1002

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?
• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?

[macportsbot]

Notifying maintainers:
@i0ntempest for port qBittorrent.

[i0ntempest]

Thank you for all this. You may merge once you sort everything out.
Also maybe revbump since you fixed development target?

[kencu]

qbittorrent raised their qt5 requirements to 5.12...so this fix won't change that fact. We may see this pattern play out fairly often, limiting the usefulness of the upgraded libcxx.

Have to consider now how fast that will obsolete qt5 < 5.12, and whether it's worth doing this at all at this point.