Fix for tools/zasm.sh being dependent on readlink -f (an issue on macOS, preventing builds) (#28)

* Fix for tools/zasm.sh being dependent on readlink -f (an issue on macOS, preventing builds)

* Wrap zasm.sh shebang in /usr/bin/env ; remove comment about BSDs

tools/zasm.sh

@@ -1,7 +1,11 @@
-#!/bin/sh
+#!/usr/bin/env bash
+
+# readlink -f doesn't work with macOS's implementation
+# so, if we can't get readlink -f to work, try python with a realpath implementation
+ABS_PATH=$(readlink -f "$0" || python -c "import sys, os; print(os.path.realpath('$0'))")
 
 # wrapper around ./emul/zasm/zasm that prepares includes CFS prior to call
-DIR=$(dirname $(readlink -f "$0"))
+DIR=$(dirname "${ABS_PATH}")
 ZASMBIN="${DIR}/emul/zasm/zasm"
 CFSPACK="${DIR}/cfspack/cfspack"
 INCCFS=$(mktemp)