[MacPorts] #63085: clang-12: compiler-rt build sometimes fails parallel building

[MacPorts]

#63085: clang-12: compiler-rt build sometimes fails parallel building
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  Reporter:  blair     |      Owner:  kencu
      Type:  defect    |     Status:  assigned
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  clang-12  |
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Comment (by kencu):

 Thanks. This is the key one, that suggested the error is the parallel
 building (which you proved by disabling it):
 {{{
 CMake Error: failed to create symbolic link '/opt/local/var/macports/build
 /_Users_blairzajac_Code_MacPorts_macports-
 ports.git_lang_llvm-12/clang-12/work/build/projects/compiler-
 rt/lib/builtins/outline_atomic_helpers.dir/outline_atomic_ldset1_2.S':
 file already exists
 }}}

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Ticket URL: <https://trac.macports.org/ticket/63085#comment:7>
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