I know that the most recent versions of POSIX specify that a C99-compliant compiler should (optionally) be present and called c99. Similarly, older versions of POSIX used to specify an optional c89 command to exist as part of the "C-Language Development Utilities".
However, I'm having a hard time finding any reference to cc. Is this command mentioned somewhere in the POSIX standard or just a convention?
The original POSIX 1003.1 (published in 1988) specified a cc utility. The Single Unix Specification version 2 (1997) included both cc and c89. The name c89 was introduced to be a standard dialect of C. The name cc was kept but marked as legacy and declared to be an unspecified dialect of C. Many vendors shipped a compiler that defaulted to K&R C (i.e. pre-ANSI C) under the name cc. You might note that cc is mandatory while c89 is part of the C language development option. It was common to have a C compiler under the name cc that was only really capable of compiling kernel drivers, and commercial unices often charged extra for a proper C compiler.
POSIX 1003.1-2001 (Single Unix v3) specifies c99 specifies instead of c89, to use an updated standard dialect of C. You can see some editorial traces left from a draft that included a cc utility as well, but cc was removed from the specification. POSIX 1003.1-2008 (Single Unix v4) again just has c99
cc they made a C compiler optional as part of the "C-Language Development Utilities" instead of required? c11 or c17 - they all seem to have stuck with c99. c17 command. Moreover, it also specifies how to create shared objects with this command. c17 utility of POSIX.1-2024 standard
c89when the two (cc/c89) were considered to be the same thing. Finding an authoritative source for that will be hard, since the POSIX documentation eliminates most of the historical information.