test1175: fix to run, and fix docs to pass

Fix test1175 to pass the correct source root directory.
Before this patch this caused a silent failure and the tests didn't run.

With this fixed, it detected 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
```

Fix them by:
- marking `CURLE_FUNCTION_NOT_FOUND` deprecated by 7.53.0
- marking `CURLE_HTTP_POST_ERROR` deprecated by 7.56.0
- marking `CURLE_TELNET_OPTION_SYNTAX` deprecated by 7.78.0
- documenting `CURLM_CALL_MULTI_SOCKET` as a synonym for
  `CURLM_CALL_MULTI_PERFORM`

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

Cherry-picked from #17877

docs/libcurl/libcurl-errors.md

@@ -505,6 +505,11 @@ 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)
+
+Synonym for *CURLM_CALL_MULTI_PERFORM*.
+(Added in 7.15.5)
+
 ## CURLM_OK (0)
 
 Things are fine.

docs/libcurl/symbols-in-versions

@@ -263,14 +263,14 @@ CURLE_FTP_WEIRD_PASV_REPLY      7.1
 CURLE_FTP_WEIRD_SERVER_REPLY    7.1           7.51.0
 CURLE_FTP_WEIRD_USER_REPLY      7.1           7.17.0
 CURLE_FTP_WRITE_ERROR           7.1           7.17.0
-CURLE_FUNCTION_NOT_FOUND        7.1
+CURLE_FUNCTION_NOT_FOUND        7.1           7.53.0
 CURLE_GOT_NOTHING               7.9.1
 CURLE_HTTP2                     7.38.0
 CURLE_HTTP2_STREAM              7.49.0
 CURLE_HTTP3                     7.68.0
 CURLE_HTTP_NOT_FOUND            7.1           7.10.3
 CURLE_HTTP_PORT_FAILED          7.3           7.12.0
-CURLE_HTTP_POST_ERROR           7.1
+CURLE_HTTP_POST_ERROR           7.1           7.56.0
 CURLE_HTTP_RANGE_ERROR          7.1           7.17.0
 CURLE_HTTP_RETURNED_ERROR       7.10.3
 CURLE_INTERFACE_FAILED          7.12.0
@@ -321,7 +321,7 @@ CURLE_SSL_ISSUER_ERROR          7.19.0
 CURLE_SSL_PEER_CERTIFICATE      7.8           7.17.1
 CURLE_SSL_PINNEDPUBKEYNOTMATCH  7.39.0
 CURLE_SSL_SHUTDOWN_FAILED       7.16.1
-CURLE_TELNET_OPTION_SYNTAX      7.7
+CURLE_TELNET_OPTION_SYNTAX      7.7           7.78.0
 CURLE_TFTP_DISKFULL             7.15.0        7.17.0
 CURLE_TFTP_EXISTS               7.15.0        7.17.0
 CURLE_TFTP_ILLEGAL              7.15.0

tests/data/test1175

@@ -18,7 +18,7 @@ Verify that symbols-in-versions and libcurl-errors.3 are in sync
 </name>
 
 <command type="perl">
-%SRCDIR/test1175.pl %SRCDIR
+%SRCDIR/test1175.pl %SRCDIR/..
 </command>
 </client>