geda-gaf dependency error, it fails to install guile18 if absent from the system

[wilya7]

While doing a port -f clean --all all i got the following error:

Error: geda-gaf: Error executing useguile18: Package guile-1.8 was not found in the pkg-config search path.
Perhaps you should add the directory containing `guile-1.8.pc'
to the PKG_CONFIG_PATH environment variable
No package 'guile-1.8' found

if I do try to install geda-gaf without installing first guile18, this is what I get:

Hasbeen-MBP:~ cfusco$ sudo port -d install geda-gaf
Password:
DEBUG: Copying /Users/cfusco/Library/Preferences/com.apple.dt.Xcode.plist to /opt/local/var/macports/home/Library/Preferences
DEBUG: Changing to port directory: /opt/local/var/macports/sources/rsync.macports.org/release/tarballs/ports/science/geda-gaf
DEBUG: OS darwin/16.7.0 (Mac OS X 10.12) arch i386
DEBUG: adding the default universal variant
DEBUG: Reading variant descriptions from /opt/local/var/macports/sources/rsync.macports.org/release/tarballs/ports/_resources/port1.0/variant_descriptions.conf
DEBUG: Executing variant useguile18 provides useguile18
DEBUG: Package guile-1.8 was not found in the pkg-config search path.
Perhaps you should add the directory containing `guile-1.8.pc'
to the PKG_CONFIG_PATH environment variable
No package 'guile-1.8' found
    while executing
"exec ${prefix}/bin/pkg-config --cflags guile-1.8"
    (procedure "variant-useguile18" line 12)
    invoked from within
"variant-useguile18"
Error: geda-gaf: Error executing useguile18: Package guile-1.8 was not found in the pkg-config search path.
Perhaps you should add the directory containing `guile-1.8.pc'
to the PKG_CONFIG_PATH environment variable
No package 'guile-1.8' found
DEBUG: Error evaluating variants
    while executing
"error "Error evaluating variants""
    (procedure "mportopen" line 50)
    invoked from within
"mportopen $porturl [array get options] [array get requested_variations]"
Error: Unable to open port: Error evaluating variants

This is my system:

Hasbeen-MBP:~ cfusco$ sw_vers 
ProductName:	Mac OS X
ProductVersion:	10.12.6
BuildVersion:	16G29

[kencu (Ken)]

Yes, I was being perhaps a bit too fancy trying to get the CFLAGS just perfect. However, if you have pkg-config installed, but not yet guile18, it fails. I'll fix it today. - K

[kencu (Ken)]

In 243ad418601fcc4a27d06233f8c910ca07b45635/macports-ports:

geda-gaf: rework build against guile18

change to configure args instead of ENV vars
add test for installed guile18 before pkg-config is run
closes: #54865