build: include curlx headers directly in src and tests

To include what's actually used.

Also:
- drop unused includes.
- scope includes where possible.
- drop `curlx/curlx.h` umbrella header.
- config2setopts: include `netinet/in.h` for Cygwin/MSYS2.
  Previously included by chance via an unused curlx include.

Closes #20776

src/config2setopts.c

@@ -40,6 +40,10 @@
 #include "tool_helpers.h"
 #include "tool_version.h"
 
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h> /* IPPROTO_IPV6 */
+#endif
+
 #define BUFFER_SIZE 102400L
 
 #ifdef IP_TOS

src/tool_doswin.c

@@ -25,6 +25,9 @@
 
 #if defined(_WIN32) || defined(MSDOS)
 
+#include "curlx/basename.h" /* for curlx_basename() */
+#include "curlx/version_win32.h" /* for curlx_verify_windows_version() */
+
 #ifdef _WIN32
 #  include <tlhelp32.h>
 #elif !defined(__DJGPP__) || (__DJGPP__ < 2)  /* DJGPP 2.0 has _use_lfn() */

src/tool_operate.c

@@ -23,6 +23,8 @@
  ***************************************************************************/
 #include "tool_setup.h"
 
+#include "curlx/nonblock.h" /* for curlx_nonblock() */
+
 #ifdef HAVE_LOCALE_H
 #  include <locale.h>
 #endif

src/tool_setup.h

@@ -45,7 +45,17 @@ extern FILE *tool_stderr;
  * curl tool certainly uses libcurl's external interface.
  */
 
-#include <curlx/curlx.h>
+#include "curlx/base64.h" /* for curlx_base64* */
+#include "curlx/dynbuf.h" /* for curlx_dyn_*() */
+#include "curlx/fopen.h" /* for curlx_f*() */
+#include "curlx/multibyte.h" /* for curlx_convert_*() */
+#include "curlx/strcopy.h" /* for curlx_strcopy() */
+#include "curlx/strdup.h" /* for curlx_memdup*() */
+#include "curlx/strerr.h" /* for curlx_strerror() */
+#include "curlx/strparse.h" /* for curlx_str_* parsing functions */
+#include "curlx/timediff.h" /* for timediff_t type and related functions */
+#include "curlx/timeval.h" /* for curlx_now type and related functions */
+#include "curlx/wait.h" /* for curlx_wait_ms() */
 
 /*
  * Platform specific stuff.