test1175: fix to run, and fix documentation issues detected

Fix test 1175 by passing the source root directory (was: tests).

Before this patch this caused silent Perl warnings and returning success
without executing the tests, due to:
```
readline() on closed filehandle $f at ../../tests/test1175.pl line 55.
readline() on closed filehandle $f at ../../tests/test1175.pl line 39.
```

Running the test revealed these issues:
```
CURLE_FUNCTION_NOT_FOUND is not in libcurl-errors.md
CURLE_HTTP_POST_ERROR is not in libcurl-errors.md
CURLE_TELNET_OPTION_SYNTAX is not in libcurl-errors.md
CURLM_CALL_MULTI_SOCKET is not in libcurl-errors.md
```

Apply fixes:
- mark `CURLE_FUNCTION_NOT_FOUND` deprecated by 7.53.0
- mark `CURLE_HTTP_POST_ERROR` deprecated by 7.56.0
- mark `CURLE_TELNET_OPTION_SYNTAX` deprecated by 7.78.0
- document `CURLM_CALL_MULTI_SOCKET` as a synonym for
  `CURLM_CALL_MULTI_PERFORM`
- test1477: exclude `CURLM_CALL_MULTI_SOCKET`.

But, these weren't officially deprecated. It may need more updates
to reflect that in other places, or fix the issues differently.

Follow-up to 66ec950004cd45350ad81134557be86391397048 #12424
Follow-up to 74f441c6d31ff8f8bfd242c3d4027d4a56230ce1 #4628

Cherry-picked from #17877
Closes #17880

1 files changed, 6 insertions, 0 deletions

diff --git a/docs/libcurl/libcurl-errors.md b/docs/libcurl/libcurl-errors.md
index ed2f4ca5a..773601dae 100644
--- a/docs/libcurl/libcurl-errors.md
+++ b/docs/libcurl/libcurl-errors.md
@@ -505,6 +505,12 @@ between. Before version 7.20.0 (released on February 9 2010) this could be retur
 curl_multi_perform(3), but in later versions this return code is never
 used.
 
+## CURLM_CALL_MULTI_SOCKET (-1)
+
+An alias for *CURLM_CALL_MULTI_PERFORM*. Never returned by modern libcurl
+versions.
+(Added in 7.15.5)
+
 ## CURLM_OK (0)
 
 Things are fine.