Add helper script to fix macOS libEvent packaging

fix_macOS_libevent_rpath.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+# libEvent uses absolute paths inside the dylibs on macOS. It's been politely
+# suggested they switch to a more standard relative rpath scheme, but so far
+# the maintainers are not keen, and instead recommend a post-build
+# fix-up step using installnametool, so that's what this script does.
+#
+# see: https://github.com/libevent/libevent/issues/920
+
+echo "Editing libEvent rpaths in: $1"
+
+pushd $1
+names="event|event_core|event_extra"
+
+find -E . -type f -depth 1 \
+      -regex "\\./lib($names)"'-([0-9]+\.[0-9]+\.[0-9]+)\.dylib$' | \
+while read filename; do
+    filename="${filename#./}"      # get rid of the './'
+
+    # extract the version part using sed, yuck
+    version=$(printf "%s" "$filename" | sed -Ee 's@.*-([0-9]+\.[0-9]+\.[0-9]+)\.dylib$@\1@')
+
+    echo "Found: '$filename'. Version is: $version"
+
+    install_name_tool -id "@rpath/${filename}" ${filename}
+
+    # change primary and 'core' library references
+    # if a reference is not found, it's not touched, so we can apply these each time
+    install_name_tool -change "$PWD/libevent_core-$version.dylib" "@rpath/libevent_core-$version.dylib" ${filename}
+    install_name_tool -change "$PWD/libevent-$version.dylib" "@rpath/libevent-$version.dylib" ${filename}
+done
+
+popd
+
+echo "Done fixing install names for libEvent"