[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 RJVB):

 I don't understand your point 2, esp. not the point of incorrect dylib
 IDs. I'm not modifying those. Yes, the point of the +with_libgcc variant
 is to install gcc as one would normally do, and let port:libgcc install
 symlinks instead of actual library files, which point to the libraries
 installed by port:gcc7. That's enough to satisfy the dependencies of the
 binary builds provided by the build bots.

 > For the +libcxx changes... is g++ expected to be compatible with libc++?

 Why would it not be, provided you use the correct headerfiles? My changes
 basically implement the instructions given on
 http://libcxx.llvm.org/docs/UsingLibcxx.html#using-libc-with-gcc so there
 is some form of support for using libc++ with g++. In fact, I understand
 that libc++ aims to be a modern alternative to libstdc++, not something
 that is usable only with llvm.

 I have asked on the GCC ML and it was confirmed that this change will also
 be considered for inclusion into gcc provided it doesn't hardcode the
 choice of runtime but adds a -stdlib option like clang has. I don't
 particularly mind trying to get that done properly before presenting the
 patch upstream (helping hands appreciated). But I'd really like to be able
 to argue that it has been tested by others before presenting it upstream.

--
Ticket URL: <https://trac.macports.org/ticket/54773#comment:3>
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