[MacPorts] #56619: I ran "sudo port selfupdate" and now I cannot install any ports without an error

[MacPorts]

#56619: I ran "sudo port selfupdate" and now I cannot install any ports without an
error
--------------------------------+--------------------
 Reporter:  JulioDavidMartinez  |      Owner:  (none)
     Type:  defect              |     Status:  new
 Priority:  High                |  Milestone:
Component:  base                |    Version:  2.5.2
 Keywords:                      |       Port:
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 Here is the log:\\

 System headers do not appear to be installed. Most ports should build
 correctly, but if you experience problems due to a port depending on
 system headers, please file a ticket at https://trac.macports.org.\\

 Warning: You can install them as part of the Xcode Command Line Tools
 package by running `xcode-select --install'.\\

 --->  Computing dependencies for fontforgeError: Unable to determine
 location of a macOS SDK.\\

 Error: Unable to execute port: can't read "configure.sdkroot": Unable to
 determine location of a macOS SDK.\\


 It always asks me to install `xcode-select --install`, I have installed it
 like 50 times.
 This line is new since the update:\\

 Unable to execute port: can't read "configure.sdkroot":

 I have no idea what file this is nor where to locate it.
 How can I fix this?
 Please help.
 Im running Yosemite.
 I have XCode installed and the XCode Tools.
 I have been running MacPorts successfully for years on this station.
 Ever since the selfupdate today it broke.
 I cannot upgrade to High Sierra because we use an XSan system over fibre
 and the newer versions of OS X don't support our setup.
 I even tried uninstalling all my ports and deleting macports all together
 and then re-installing from scratch.
 Still gives me that error about the config file.

-- 
Ticket URL: <https://trac.macports.org/ticket/56619>
MacPorts <https://www.macports.org/>
Ports system for macOS