[MacPorts] #53445: port:mlt/mlt-qt5 fixes

[MacPorts]

#53445: port:mlt/mlt-qt5 fixes
-------------------------+-----------------
 Reporter:  RJVB         |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:  haspatch     |       Port:  mlt
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 The attached patch addresses the following issues:

 - qt5.depends_component is now available officially so the local copy can
 be removed.
 - mlt 6.4.1 doesn't (sufficiently) honour the compiler and build settings
 that the Portfile passed in via the environment. This is addressed by
 amending the generated config.mak file.
 - From 5.7.0 onwards Qt5 requires C++11 which at least on 10.9.5 must be
 requested specifically (with mlt's build system). Doing this requires the
 previous fix. The C++11 option is added explicitly only when Qt >= 5.7.0
 is active but could also be activated unconditionally on platforms that
 have libc++.

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Ticket URL: <https://trac.macports.org/ticket/53445>
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