Fix Windows.h case on Linux: use lowercase windows.h

On Linux (case-sensitive filesystem) MinGW-w64 installs the header as
windows.h (lowercase) while comm.h included <Windows.h> (capital W),
causing a fatal compile error when cross-compiling for Windows.

Changed to <windows.h> which works on both Linux/MinGW-w64 and native
Windows/MSVC (Windows header includes are case-insensitive on NTFS).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile.windows

@@ -117,7 +117,7 @@ check-tools:
 	  echo "  Debian:  sudo apt install mingw-w64"; \
 	  echo "  Fedora:  sudo dnf install mingw64-gcc"; \
 	  echo ""; exit 1; }
-	@echo '#include <windows.h>' | $(CC) -x c - -fsyntax-only 2>/dev/null || { \
+	@echo '#include <windows.h>' | $(CC) -x c - -fsyntax-only -Wno-pragma-once-outside-header 2>/dev/null || { \
 	  echo ""; \
 	  echo "ОШИБКА: Windows API заголовки не найдены."; \
 	  echo "Установите пакет с заголовками MinGW-w64:"; \

comm.h

@@ -33,7 +33,7 @@ warren@wpratt.com
 #endif
 
 #ifdef _WIN32
-#include <Windows.h>
+#include <windows.h>
 #include <process.h>
 #include <intrin.h>
 #endif