Add a script to set up PKG_CONFIG_PATH for certain packages on macOS.

test/setup_pkgconfig_with_homebrew.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# Homebrew does not put the .pc files in a common place that pkg-config can find.
+# This script sets up the PKG_CONFIG_PATH so that the packages can be found by Natalie.
+# You can run this prior to running `bin/natalie` or `rake test` or whatever.
+#
+# Usage:
+#
+#     eval(test/setup_pkgconfig_with_homebrew.sh)
+
+set -e
+
+packages=("libyaml")
+
+if ! type -P brew &>/dev/null; then
+  echo "Could not find $(brew) command. This script assumes you have Homebrew installed."
+  exit 1
+fi
+
+for package in ${packages[@]}; do
+  PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$(brew --prefix $package)/lib/pkgconfig"
+done
+
+echo "export PKG_CONFIG_PATH=\"$PKG_CONFIG_PATH\""