Failed to build graphviz: command execution failed

[Michael Newman]

> On Sep 3, 2020, at 22:01, Ryan Schmidt <ryandesign at macports.org> wrote:
> 
> There have been a few other reports lately of graphviz build failures for other reasons; if you're experiencing a graphviz build failure, see if one of them applies.

I spent some time searching around, but all I found were other instance of graphviz related tickets, the details of which are beyond my ability to comprehend.

When graphviz builds, I get this warning:

Warning: cltversion: The Command Line Tools are installed, but MacPorts cannot determine the version.
Warning: cltversion: For a possible fix, please see: https://trac.macports.org/wiki/ProblemHotlist#reinstall-clt

So, I run this:

MrMuscle:~ mnewman$ xcode-select --install
xcode-select: error: command line tools are already installed, use "Software Update" to install updates

But, that doesn't fix the "MacPorts cannot determine the version" warning. 

Xcode is at Version 11.7 (11E801a)

The details:

--->  Computing dependencies for graphviz
--->  Fetching archive for graphviz
--->  Attempting to fetch graphviz-2.40.1_3+pangocairo+x11.darwin_19.x86_64.tbz2 from http://jog.id.packages.macports.org/macports/packages/graphviz
--->  Attempting to fetch graphviz-2.40.1_3+pangocairo+x11.darwin_19.x86_64.tbz2 from https://kmq.jp.packages.macports.org/graphviz
--->  Attempting to fetch graphviz-2.40.1_3+pangocairo+x11.darwin_19.x86_64.tbz2 from http://nue.de.packages.macports.org/graphviz
--->  Building graphviz
Error: Failed to build graphviz: command execution failed
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_graphics_graphviz/graphviz/main.log for details.
Error: Follow https://guide.macports.org/#project.tickets to report a bug.

The log file referred to is rather large (almost 1MB) and incomprehensible to me.

I don't know how to proceed from here.