[MacPorts] #60564: Make setting known_fail yes also prevent looking for archives

[MacPorts]

#60564: Make setting known_fail yes also prevent looking for archives
-------------------------+-----------------------------
 Reporter:  ryandesign   |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:  MacPorts Future
Component:  base         |    Version:  2.6.2
 Keywords:               |       Port:
-------------------------+-----------------------------
 Some ports do this (this is from gcc49):

 {{{
 if {${os.platform} eq "darwin" && ([vercmp $xcodeversion 9.0] > 0)} {
     known_fail      yes
     depends_lib
     depends_run
     archive_sites
     pre-fetch {
         ui_error "building ${name} is not supported with Xcode 9 or
 greater"
         return -code error {unsupported platform}
     }
 }
 }}}

 In other words in addition to setting `known_fail yes` and printing an
 error message, it clears `archive_sites`. This is probably intended to
 stop MacPorts from spending time checking for an archive that we already
 know does not exist. Maybe MacPorts base could arrange for `archive_sites`
 to be cleared automatically when `known_fail yes` is used, or it could use
 some other method to prevent checking for the presence of archives.

 I'll file a separate ticket about clearing dependencies.

-- 
Ticket URL: <https://trac.macports.org/ticket/60564>
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