Hello Pedro:
Do not set:
AS=usr/ccs/bin/as:$PATH
instead set:
PATH=/usr/ccs/bin:$PATH
that is, put /usr/ccs/bin early on PATH so the assembler "as" can be found.
Afterwords, verify that "as" can be found by entering:
type as
You could see a result like this:
as is /usr/ccs/bin/as