===============================================================================

You should exports the following enviropment variables:

export CC65_INC=%%PREFIX%%/lib/cc65/include
export CC65_LIB=%%PREFIX%%/lib/cc65/lib

or for csh users:

setenv CC65_INC %%PREFIX%%/lib/cc65/include
setenv CC65_LIB %%PREFIX%%/lib/cc65/lib

===============================================================================