[MacPorts] #63150: mkvtoolnix @58.0.0_0+qtgui: build fails during configure

[MacPorts]

#63150: mkvtoolnix @58.0.0_0+qtgui: build fails during configure
-----------------------+------------------------
 Reporter:  klanchman  |      Owner:  ryandesign
     Type:  defect     |     Status:  assigned
 Priority:  Normal     |  Milestone:
Component:  ports      |    Version:  2.7.1
 Keywords:             |       Port:
-----------------------+------------------------
 When upgrading from mkvtoolnix 57 to 58, compilation fails at the
 configure step due to seemingly missing Boost prerequisites:

 {{{
 :info:configure configure: error: Boost's multi-precision library is
 required but wasn't found
 }}}

 However, the `boost176` port is installed and I see a directory that seems
 related, `/opt/local/libexec/boost/1.76/include/boost/multiprecision/`.

 Environment details:
 * macOS 11.4 (20F71)
 * Xcode 12.5.1 (12E507) - installed at nonstandard path
 `/Applications/Xcode/Xcode_12.5.1.app`
 * 3 different machines, all with Intel CPUs

-- 
Ticket URL: <https://trac.macports.org/ticket/63150>
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