plplot510: _pkg_check_modules_internal Macro invoked with incorrect arguments

[ryandesign (Ryan Carsten Schmidt)]

​plplot510 doesn't configure. There are a lot of suspicious warnings in the log, but the errors seem to be:

application-specific initialization failed: no display name and no $DISPLAY environment variable
Error in startup script: no display name and no $DISPLAY environment variable
    while executing
"load /opt/local/lib/libtk8.6.dylib Tk"
    ("package ifneeded Tk 8.6.10" script)
    invoked from within
"package require Tk"
    invoked from within
"puts -nonewline [package require Tk]"
    (file "/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_science_plplot510/plplot510/work/build/CheckTK_VERSION.tcl" line 1)

CMake Error at cmake/modules/pkg-config.cmake:100 (_pkg_check_modules_internal):
  _pkg_check_modules_internal Macro invoked with incorrect arguments for
  macro named: _pkg_check_modules_internal
Call Stack (most recent call first):
  cmake/modules/pango.cmake:23 (pkg_check_pkgconfig)
  cmake/modules/plplot.cmake:535 (include)
  CMakeLists.txt:111 (include)

​Same for plplot510-single.

[ryandesign (Ryan Carsten Schmidt)]

This problem still happens today. Probably nobody has been able to install plplot510 or plplot510-single in at least 10 months.

Are they still needed or should they be removed? plplot510 was originally created for the benefit of gnudatalanguage but gnudatalanguage now uses the main plplot port and I can't find anything else in MacPorts that depends on plplot510 or plplot510-single.