cmake: enable -Wall for MSVC when PICKY_COMPILER=ON

Enable it for `_MSC_VER <= 1943`.

Omit it for not yet CI-tested MSVC versions, to avoid hitting unfixed
warnings emitted by future toolchain releases. It means we need
to explicitly opt-in to newer MSVC versions while fixing any new issues.

The newly enabled warnings did not reveal new issues. It hints that we
catch those with clang/gcc. Yet, these warnings may be useful for local
development done with MSVC.

Also:
- disable and document warnings that don't seem useful, unactionable,
  or unfixable.
- disable and document warnings found in Windows SDK headers.
- tidy up a few comments, also to avoid
  `-Wdocumentation-unknown-command`, part of llvm/clang `-Wall`.
  ```
  lib\dynhds.h(159,29): error : unknown command tag name [-Werror,-Wdocumentation-unknown-command]
  lib\ftp.c(337,15): error : unknown command tag name [-Werror,-Wdocumentation-unknown-command]
  ```
  (This patch did not end up enabling `-Wall` for clang-cl.)

Closes #17050

lib/dynhds.h

@@ -156,14 +156,14 @@ CURLcode Curl_dynhds_cadd(struct dynhds *dynhds,
 
 /**
  * Add a single header from an HTTP/1.1 formatted line at the end. Line
- * may contain a delimiting \r\n or just \n. Any characters after
+ * may contain a delimiting CRLF or just LF. Any characters after
  * that will be ignored.
  */
 CURLcode Curl_dynhds_h1_cadd_line(struct dynhds *dynhds, const char *line);
 
 /**
  * Add a single header from an HTTP/1.1 formatted line at the end. Line
- * may contain a delimiting \r\n or just \n. Any characters after
+ * may contain a delimiting CRLF or just LF. Any characters after
  * that will be ignored.
  */
 CURLcode Curl_dynhds_h1_add_line(struct dynhds *dynhds,

lib/ftp.c

@@ -330,8 +330,7 @@ static void freedirs(struct ftp_conn *ftpc)
 }
 
 #ifdef CURL_PREFER_LF_LINEENDS
-/***********************************************************************
- *
+/*
  * Lineend Conversions
  * On ASCII transfers, e.g. directory listings, we might get lines
  * ending in '\r\n' and we prefer just '\n'.