[MacPorts] #54773: port:libgcc/port:gcc7: proposed modifications, efficiency + libc++ support

[MacPorts]

#54773: port:libgcc/port:gcc7: proposed modifications, efficiency + libc++ support
--------------------------+----------------------
  Reporter:  RJVB         |      Owner:
      Type:  enhancement  |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:  haspatch
      Port:  gcc7 libgcc  |
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Comment (by jeremyhu):

 For the assembler issue, the problem is that MacPorts doesn't allow us to
 solve it easily.  Ideally, the cctools port would have a runtime
 dependency on a specific version of clang, which it would use for -q.
 However, llvm and clang ports require cctools at build time on older
 versions of macOS.  There's no *real* dependency cycle there, but MacPorts
 sees one because we have no notion of dependencies that must be present at
 runtime but are not needed at build time.

 We could solve this by providing a way to pass the path to clang to as.
 as/driver.c could support --clang= command line argument or just
 getenv("CLANG").

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Ticket URL: <https://trac.macports.org/ticket/54773#comment:2>
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