[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  |
--------------------------+----------------------

Comment (by RJVB):

 > > > is there a hard reason why I shouldn't simply use /usr/bin/as -q
 > >
 > > Because that will only work well on Xcode 7 or 8 and newer.
 >
 > Care to give a bit more detail?
 > My Xcode 6.something packs a clang 3.5 version and by the time you get
 around to replying I should have confirmation if gcc itself builds using
 that version for assembler or not.


 Well indeed. GCC itself builds fine with the `as` from Xcode 6.2 (using a
 non-bootstrap build and the 10.9.5 system clang version).
 However, the resulting compiler failed to build some Qt 5.8 code (a bit
 surprising because that same code builds fine with the system clang).

 As a side-note: full GCC build configured with `--disable-bootstrap` using
 clang-mp-4.0 is over 4x faster than the `bootstrap-lean` procedure used
 normally, the build directory is more than 2x smaller (*after* HFS
 compression!) and the resulting binary image (xz-compressed tarball) is
 10% smaller. I still need to do a few comparisons of compiler performance
 (the bootstrapped version might be faster according to the docs) but these
 figures justify a `+quick` variant IMHO.

--
Ticket URL: <https://trac.macports.org/ticket/54773#comment:14>
MacPorts <https://www.macports.org/>
Ports system for macOS