windows: drop dupe macros, detect CURL_OS for WinCE ARM, indentation

- setup-win32: drop duplicate `WIN32_LEAN_AND_MEAN` and `NOGDI` macros
  (set earlier in `curl_setup.h`)

- config-win32ce: detect ARM for `CURL_OS` macro.
  Based on: https://cegcc.sourceforge.net/docs/details.html
  It should also apply to MSVC. (untested)

- indentation.

Closes #16029

tests/libtest/lib556.c

@@ -28,13 +28,13 @@
 
 /* For Windows, mainly (may be moved in a config file?) */
 #ifndef STDIN_FILENO
-  #define STDIN_FILENO 0
+#define STDIN_FILENO 0
 #endif
 #ifndef STDOUT_FILENO
-  #define STDOUT_FILENO 1
+#define STDOUT_FILENO 1
 #endif
 #ifndef STDERR_FILENO
-  #define STDERR_FILENO 2
+#define STDERR_FILENO 2
 #endif
 
 CURLcode test(char *URL)