include: avoid recursive macros

[vszakats]

To fix potential -Wdisabled-macro-expansion warnings when using these
macros within other macros. Fixing for example:

lib/doh.c:328:3: error: disabled expansion of recursive macro [clang-diagnostic-disabled-macro-expansion,-warnings-as-errors]
  328 |   ERROR_CHECK_SETOPT(CURLOPT_URL, url);
      |   ^
lib/doh.c:271:14: note: expanded from macro 'ERROR_CHECK_SETOPT'
  271 |     result = curl_easy_setopt((CURL *)doh, x, y);       \
      |              ^
include/curl/curl.h:3332:44: note: expanded from macro 'curl_easy_setopt'
 3332 | #define curl_easy_setopt(handle,opt,param) curl_easy_setopt(handle,opt,param)
      |                                            ^
[...]

Also update comments on why curl continues to disable
-Wdisabled-macro-expansion and -Wused-but-marked-unused warnings.

Follow-up to 92f215f #18477

---

Disabling this warning probably should be done regardless of
picky warnings enabled or not. That's likely true for other no
options too, thus not tackled in this PR.

• enable the warnings when possible. → TRIED, but these warnings
  pop up due to 3rd-party headers, e.g. Linux glibc (stdio/stderr),
  MUSL (sa_handler) and in OpenSSL 3 (due to ossl_unused used
  in its public headers). Meaning it's not possible to enable these.

[vszakats]

CM libressl Fil-C:

In file included from /home/runner/work/curl/curl/lib/conncache.c:36:
/home/runner/work/curl/curl/lib/sigpipe.h:59:12: error: disabled expansion of recursive macro [-Werror,-Wdisabled-macro-expansion]
   59 |     action.sa_handler = SIG_IGN;
      |            ^
/home/runner/filc/build/bin/../../pizfix/include/signal.h:178:35: note: expanded from macro 'sa_handler'
  178 | #define sa_handler   __sa_handler.sa_handler
      |                                   ^
1 error generated.

https://github.com/curl/curl/actions/runs/22039030172/job/63676732424?pr=20597#step:42:45

CM clang HTTP/3 clang-tidy:

/Users/runner/work/curl/curl/lib/doh.c:328:3: error: disabled expansion of recursive macro [clang-diagnostic-disabled-macro-expansion,-warnings-as-errors]
  328 |   ERROR_CHECK_SETOPT(CURLOPT_URL, url);
      |   ^
/Users/runner/work/curl/curl/lib/doh.c:271:14: note: expanded from macro 'ERROR_CHECK_SETOPT'
  271 |     result = curl_easy_setopt((CURL *)doh, x, y);       \
      |              ^
/Users/runner/work/curl/curl/include/curl/curl.h:3332:44: note: expanded from macro 'curl_easy_setopt'
 3332 | #define curl_easy_setopt(handle,opt,param) curl_easy_setopt(handle,opt,param)
      |                                            ^
[...]

https://github.com/curl/curl/actions/runs/22039030164/job/63676732284?pr=20597#step:11:77

linux-mingw, CM clang-tidy:

/home/runner/work/curl/curl/lib/mprintf.c:685:4: error: 'snprintf' was marked unused but was used [clang-diagnostic-used-but-marked-unused,-warnings-as-errors]
  685 |   (snprintf)(work, BUFFSIZE, formatbuf, dnum);
      |    ^
1 warning generated.

https://github.com/curl/curl/actions/runs/22041102952/job/63682054988?pr=20597#step:8:103

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