Fix macOS PATH being rewritten in /etc/zprofile

macOS is obnoxious and overwrites the PATH from a users ~/.zshenv, which is
sourced first, in /etc/zprofile by calling `/usr/libexec/path_helper -s` so
this is required so that PATH is once again set to the desired value.

zshenv

@@ -12,7 +12,7 @@ SAVEHIST=5000
 REPORTTIME=5
 
 # Add Homebrew python to PATH on macOS if present
-[ "`uname`" = "Darwin" ] && [ -d /usr/local/opt/python/libexec/bin ] &&
+[ -d /usr/local/opt/python/libexec/bin ] && \
   PATH=/usr/local/opt/python/libexec/bin:$PATH
 
 # Add ~/.local to the environment
@@ -21,6 +21,20 @@ PATH=$HOME/.local/bin:$PATH
 MANPATH=$HOME/.local/share/man:$MANPATH
 INFOPATH=$HOME/.local/share/info:$INFOPATH
 
+if [ `uname` = Darwin ]; then
+  [ -f /usr/local/bin/ccache ] && \
+    PATH=/usr/local/opt/ccache/libexec:$PATH
+else
+  [ -f /usr/bin/ccache ] && \
+    PATH=/usr/lib/ccache:$PATH
+fi
+
+# Remove duplicates from environment variables
+typeset -U fpath
+typeset -U PATH;      export PATH
+typeset -U MANPATH;   export MANPATH
+typeset -U INFOPATH;  export INFOPATH
+
 # Use ~/.local for pip installs on macOS
 [ "`uname`" = "Darwin" ] && export PYTHONUSERBASE=$HOME/.local