[illumos-Developer] __FUNCTION__ in illumos

[Albert Lee]

The non-standard __FUNCTION__ macro is not available in Sun Studio 12,
the current compiler supported by illumos, although it is available in
gcc and Sun Studio 12.1. It is equivalent to C99's __func__, which is
available in Sun Studio 12.

illumos is dependent on Net-SNMP headers (from SFW). illumos fails to
build on OpenIndiana build 148 because of a build-time feature test in
Net-SNMP that causes a generated header to use __FUNCTION__, where
previously this was not the case: https://www.illumos.org/issues/495

While the use of __FUNCTION__ can be removed from Net-SNMP, the
references to __FUNCTION__ in illumos itself deserve a cleanup.
__FUNCTION__ itself is defined in many headers in illumos as a
compatibility measure for the headers themselves (which often have
macros involving __FUNCTION___) or occasionally their consumers in ON.
These definitions are wildly inconsistent (__func__, "", or another
string) and would need to be revisited when we migrate to a newer
compiler (even a non-Studio compiler).

As  __func__ is also used in existing code, it seems to be available
throughout ON. I'm considering the approach of adding
-D__FUNCTION=__func__ to cw and removing redefinitions of __FUNCTION__
in any private headers. I would be lying if I said my main motivation
wasn't to just work around the Net-SNMP breakage, but it seems like
this would be a general improvement over the current situation.

Does this sound reasonable to anyone?

-Albert