我尝试在MacOSX 10.9.5上使用brew安装zeromq。这是我得到的输出：
==> Downloading http://download.zeromq.org/zeromq-3.2.3.tar.gz
######################################################################## 100.0%
==> Patching
patching file tests/test_disconnect_inproc.cpp
==> ./configure --prefix=/usr/local/Cellar/zeromq/3.2.3
==> make
==> make install
==> Caveats
To install the zmq gem on 10.6 with the system Ruby on a 64-bit machine,
you may need to do:
ARCHFLAGS="-arch x86_64" gem install zmq -- --with-zmq-dir=/usr/local/opt/zeromq
==> Summary
/usr/local/Cellar/zeromq/3.2.3: 54 files, 2.3M, built in 24 seconds
在尝试执行命令（ARCHFLAGS="-arch x86_64" gem install zmq -- --with-zmq-dir=/usr/local/opt/zeromq）后，它告诉我无法安装zmq:
Fetching: zmq-2.1.4.gem (100%)
Building native extensions with: '--with-zmq-dir=/usr/local/opt/zeromq'
This could take a while...
ERROR: Error installing zmq:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb --with-zmq-dir=/usr/local/opt/zeromq
checking for zmq.h... /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:434:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:549:in `block in try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:502:in `with_werror'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:549:in `try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:1044:in `block in have_header'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:895:in `block in checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:340:in `block (2 levels) in postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:310:in `open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:340:in `block in postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:310:in `open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:336:in `postpone'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:894:in `checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:1043:in `have_header'
from extconf.rb:23:in `header?'
from extconf.rb:32:in `<main>'
Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/zmq-2.1.4 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/gems/zmq-2.1.4/./gem_make.out
有人知道这是什么问题，该如何解决吗？
xcode-select --install。 - Mark Setchell