TravisCI: add macOS system Perl to build matrix

This involves:

  - Installing cpanm via homebrew.
  - Setting ARCHFLAGS so that the correct architecture is used.

.TRAVIS.PL

@@ -53,6 +53,13 @@ sub install_libzmq(@) {
     return $prefix;
 }
 
+sub setup_cpanm_local_lib {
+    cpanm(qw(--local-lib=~/perl5 local::lib));
+    push @INC, "$ENV{HOME}/perl5/lib/perl5";
+    require local::lib;
+    local::lib->setup_env_hash_for("$ENV{HOME}/perl5");
+}
+
 sub cpanm (@) {
     eval {
         mysystem("cpanm", "--notest", @_);
@@ -89,6 +96,14 @@ sub install_libczmq {
     });
 }
 
+if( $^O eq 'darwin' ) {
+    mysystem(qw(brew install cpanm));
+    setup_cpanm_local_lib;
+
+    # set ARCHFLAGS so that `-arch i386` is not tried
+    $ENV{ARCHFLAGS} = '-arch x86_64';
+}
+
 if ( $target eq 'ZMQ-Constants' ) {
     cpanm(qw(
         inc::Module::Install

.travis.yml

@@ -1,4 +1,13 @@
 language: perl
+matrix:
+  include:
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-Constants" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-CZMQ" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-LibCZMQ1" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-LibZMQ2" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-LibZMQ3" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ-LibZMQ4" }
+    - { perl: "system", os: "osx", env: "PERL_ZMQ_TEST_TARGET=ZMQ" }
 perl:
   - "5.20"
   - "5.22"