lib: make CURLX_SET_BINMODE() and use it

Use it from libtests' `first.c` and thus also from units, and tunits.

Also:
- cmake: drop stray `curltool` lib dependency for units.
- units: stop depending on `src` headers.
- tests/server: drop depending on `src` headers.
  (the remaining one listed in the comments, `tool_xattr.h`, was not
  actually used from servers.)
- tests/server: drop duplicate curlx headers.
  (Except `warnless.h`, which is tricky on Windows.)

Closes #17672

src/tool_formparse.c

@@ -27,7 +27,6 @@
 
 #include "tool_cfgable.h"
 #include "tool_msgs.h"
-#include "tool_binmode.h"
 #include "tool_getparam.h"
 #include "tool_paramhlp.h"
 #include "tool_formparse.h"
@@ -133,7 +132,7 @@ static struct tool_mime *tool_mime_new_filedata(struct tool_mime *parent,
     curl_off_t origin;
     struct_stat sbuf;
 
-    CURL_SET_BINMODE(stdin);
+    CURLX_SET_BINMODE(stdin);
     origin = ftell(stdin);
     /* If stdin is a regular file, do not buffer data but read it
        when needed. */