[MacPorts] #63099: Selfupdate failure to 2.7.1: /usr/bin/cc can't link -lSystem

[MacPorts]

#63099: Selfupdate failure to 2.7.1: /usr/bin/cc can't link -lSystem
------------------------+--------------------
  Reporter:  gallafent  |      Owner:  (none)
      Type:  defect     |     Status:  new
  Priority:  Normal     |  Milestone:
 Component:  base       |    Version:  2.7.1
Resolution:             |   Keywords:
      Port:             |
------------------------+--------------------

Comment (by gallafent):

 Hmm. Not much present in that SDK's lib directory, certainly:
 {{{
 williamg at forth ~ % ls
 /Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk/usr/lib
 libecpg.6.5.tbd                 libecpg_compat.3.tbd
 libpgtypes.tbd                  libviolet_nocatch.tbd
 libecpg.6.tbd                   libecpg_compat.tbd
 libpq.5.6.tbd                   libviolet_verifier.tbd
 libecpg.tbd                     libpgtypes.3.4.tbd
 libpq.5.tbd                     libviolet_verifier_qemu.tbd
 libecpg_compat.3.5.tbd          libpgtypes.3.tbd                libpq.tbd
 }}}

 These were the available SDK directories at that point:
 {{{
 williamg at forth ~ % ls /Library/Developer/CommandLineTools/SDKs/
 MacOSX10.14.sdk MacOSX10.15.sdk MacOSX11.0.sdk
 }}}

 Following your advice, I went to download the Command Line Tools to
 reinstall them, and noticed there's a new point release of Xcode
 available, 2.5.1, so I installed that (drive space problems meaning I tend
 to install from the archive rather than allowing the App Store to manage
 and update my Xcode installation, it feels as if you need about 50GB free
 on the system drive if you want that to work!). After that, this is still
 true (no `libSystem.tbd` in the 11.0 SDK), but now there's some more stuff
 there:
 {{{
 williamg at forth ~ % ls /Library/Developer/CommandLineTools/SDKs
 MacOSX.sdk      MacOSX10.14.sdk MacOSX10.15.sdk MacOSX11.0.sdk
 MacOSX11.3.sdk  MacOSX11.sdk
 }}}

 … and `MacOSX.sdk` and `MacOSX11.sdk` are both symlinks to
 `MacOSX11.3.sdk` … and the selfupdate appears to proceed and complete
 successfully.

 Thanks for accurately intuiting where the problem was! I wonder what
 caused my SDK installation to be broken …

-- 
Ticket URL: <https://trac.macports.org/ticket/63099#comment:3>
MacPorts <https://www.macports.org/>
Ports system for macOS