build: tidy up and simplify setmode() detection and use

- move macro to `curl_setup.h` (from curlx), and rename.
  It's required by src, test servers, libtests. Also used by unit/tunit,
  (which is fixable but this patch doesn't touch it.)
- special-case it for Windows/Cygwin/MS-DOS.
- build: drop `setmode()`/`_setmode()` detection.
  This also avoids detecting the different `setmode()` on BSDs,
  and a lot of complexity and overhead.
- use `CURL_O_BINARY`.

Follow-up to 250d613763 #15787
Follow-up to 5e70566094 #15169

Closes #20539

src/tool_getparam.c

@@ -675,7 +675,7 @@ static ParameterError data_urlencode(const char *nextarg,
     /* a '@' letter, it means that a filename or - (stdin) follows */
     if(!strcmp("-", p)) {
       file = stdin;
-      CURLX_SET_BINMODE(stdin);
+      CURL_BINMODE(stdin);
     }
     else {
       file = curlx_fopen(p, "rb");
@@ -949,7 +949,7 @@ static ParameterError set_data(cmdline_t cmd,
     if(!strcmp("-", nextarg)) {
       file = stdin;
       if(cmd == C_DATA_BINARY) /* forced data-binary */
-        CURLX_SET_BINMODE(stdin);
+        CURL_BINMODE(stdin);
     }
     else {
       file = curlx_fopen(nextarg, "rb");