GMP fails to build on Sierra with Xcode 9.0

[lucaspettey]

The following message is received when trying to build gmp on Sierra with Xcode 9.0:

--->  Configuring gmp
Error: Failed to configure gmp, consult /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_devel_gmp/gmp/work/gmp-6.1.2/config.log

I will attach the whole log for reference, but the last lines of the log file indicate an issue with clang++:

:info:configure checking whether we are using the GNU C++ compiler... yes
:info:configure checking whether /usr/bin/clang++ -stdlib=libc++ accepts -g... yes
:info:configure checking C++ compiler /usr/bin/clang++ -stdlib=libc++ -I/opt/local/include -O2 -pedantic -fomit-frame-pointer -m64 -mtune=sandybridge -march=sandybridge... no, std iostream
:info:configure checking C++ compiler /usr/bin/clang++ -stdlib=libc++ -I/opt/local/include -g -O2... no, std iostream
:info:configure configure: error: C++ compiler not available, see config.log for details
:info:configure Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_devel_gmp/gmp/work/gmp-6.1.2" && ./configure --prefix=/opt/local --enable-cxx
:info:configure Exit code: 1

[lucaspettey]

Install log for GMP

[mf2k (Frank Schima)]

In the future, please use WikiFormatting and Cc the port maintainers (port info --maintainers gmp), if any.

[mf2k (Frank Schima)]

It builds fine on the ​buildbot.

You have not installed/updated the command line tools for Xcode 9 in High Sierra.

:info:configure configure: error: C++ compiler not available, see config.log for details

[ryandesign (Ryan Carsten Schmidt)]

Or if you have, please attach the config.log file so we can see what's going on there.