dot: add workaround for cpack problem with Cygwin

dot: add workaround for cpack problem with Cygwin

Copy the dot executable to its alias commands instead of symlinking
it. Creating symlinks to dot works fine in itself, but results in an
error like this when running cpack:

CPack Error: Problem while adding file </cygdrive/c/Users/magja/graphviz/build/_CPack_Packages/CYGWIN/ZIP/Graphviz-2.49.0~dev.20210812.2025-CYGWIN/bin/circo> to archive </cygdrive/c/Users/magja/graphviz/build/_CPack_Packages/CYGWIN/ZIP/Graphviz-2.49.0~dev.20210812.2025-CYGWIN.zip>, ERROR = Unable to read from file 'Graphviz-2.49.0~dev.20210812.2025-CYGWIN/bin/circo': Couldn't list extended attributes

circo is a symlink. Trying to read the extended attributes manually gives:

attr -l /cygdrive/c/Users/magja/graphviz/build/_CPack_Packages/CYGWIN/ZIP/Graphviz-2.49.0~dev.20210812.2025-CYGWIN/bin/circo
attr_list: Permission denied
Could not list /cygdrive/c/Users/magja/graphviz/build/_CPack_Packages/CYGWIN/ZIP/Graphviz-2.49.0~dev.20210812.2025-CYGWIN/bin/circo