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

lib/config-win32ce.h

@@ -235,8 +235,12 @@
 
 /* Define cpu-machine-OS */
 #ifndef CURL_OS
+#ifdef _M_ARM
+#define CURL_OS "arm-pc-win32ce"
+#else
 #define CURL_OS "i386-pc-win32ce"
 #endif
+#endif
 
 /* ---------------------------------------------------------------- */
 /*                            Windows CE                            */

lib/setup-win32.h

@@ -77,17 +77,6 @@
 #  if defined(_UNICODE) && !defined(UNICODE)
 #    error "_UNICODE is defined but UNICODE is not defined"
 #  endif
-/*
- * Do not include unneeded stuff in Windows headers to avoid compiler
- * warnings and macro clashes.
- * Make sure to define this macro before including any Windows headers.
- */
-#  ifndef WIN32_LEAN_AND_MEAN
-#    define WIN32_LEAN_AND_MEAN
-#  endif
-#  ifndef NOGDI
-#    define NOGDI
-#  endif
 #  include <winsock2.h>
 #  include <ws2tcpip.h>
 #  include <windows.h>