If those are really unused, aren't the checks in autotools also redundant?

aren't the checks in autotools also redundant?

You mean this part:

• curl/acinclude.m4

  Lines 1898 to 1899 in 4f2541f

  	CURL_DEFINE_UNQUOTED([CURL_TYPEOF_CURL_SOCKLEN_T], [$curl_typeof_curl_socklen_t])
  	CURL_DEFINE_UNQUOTED([CURL_SIZEOF_CURL_SOCKLEN_T], [$curl_sizeof_curl_socklen_t])

?

CURL_SIZEOF_CURL_SOCKLEN_T can be removed indeed. I think it can be done as a follow-up by a person who use autotools to build CURL and have some experience with the language, because some related code should be removed too.

I'm not so sure about CURL_TYPEOF_CURL_SOCKLEN_T. CURL_TYPEOF_CURL_SOCKLEN_T defined at compile time for almost all cases except few, so probably the value of CURL_TYPEOF_CURL_SOCKLEN_T defined by autotools sometimes used (?):

• https://github.com/curl/curl/blob/4f2541f975c97338ef421ecfeb295d9f3894c1d8/include/curl/system.h

Anyway CURL_TYPEOF_CURL_SOCKLEN_T is not used in CMake part because it's not defined here:

• https://github.com/curl/curl/blob/4f2541f975c97338ef421ecfeb295d9f3894c1d8/lib/curl_config.h.cmake

CURL_TYPEOF_CURL_SOCKLEN_T

This is defined by the public header curl/system.h so that should be totally fine to not define separately.

I can take care of the autotools cleanup of the *SOCKLEN_T macros.

Yeah, I meant that.
It would be quite surprising if one build system needed to define those and other didn't.