[zsh] Move Darwin $OSBUILD, $OSVERSION, and $HWMODEL

Move them from init_env_Darwin to their own functions in the new zsh/func/darwin
directory.

zsh/func/darwin/darwin-hardware-model

@@ -0,0 +1,11 @@
+# Eryn Wells <eryn@erynwells.me>
+
+darwin-hardware-model() {
+    if [[ -z "$darwin_hardware_model" ]]; then
+        darwin_hardware_model=`sysctl -n hw.model`
+    fi
+    return "$darwin_hardware_model"
+}
+
+darwin-hardware-model "$@"
+

zsh/func/darwin/darwin-os-build

@@ -0,0 +1,11 @@
+#!/usr/bin/env zsh
+# Eryn Wells <eryn@erynwells.me>
+
+darwin-os-build() {
+    if [[ -z "$darwin_os_build" ]]; then
+        darwin_os_build=`sysctl -n kern.osversion`
+    fi
+    echo "$darwin_os_build"
+}
+
+darwin-os-build "$@"

zsh/func/darwin/darwin-os-version

@@ -0,0 +1,11 @@
+#!/usr/bin/env zsh
+# Eryn Wells <eryn@erynwells.me>
+
+darwin-os-version() {
+    if [[ -z "$darwin_os_version" ]]; then
+        darwin_os_version=`sysctl -n kern.osproductversion`
+    fi
+    echo "$darwin_os_version"
+}
+
+darwin-os-version "$@"

zsh/func/init_env_darwin

@@ -4,10 +4,6 @@
 autoload append_to_path
 autoload prepend_to_path
 
-export OSBUILD=`sysctl -n kern.osversion`
-export OSVERSION=`sysctl -n kern.osproductversion`
-export HWMODEL=`sysctl -n hw.model`
-
 export XCODE_LIBRARY="$HOME/Library/Developer/Xcode"
 export XCODE_DERIVED_DATA="$XCODE_LIBRARY/DerivedData"
 export XCODE_INSTALLS="$XCODE_LIBRARY/Installs"