Fix platform_compat.h - remove duplicate definitions for MSYS2

- Remove duplicate struct pollfd (already in winsock2.h)
- Remove duplicate struct timezone (already in time.h)
- Remove duplicate nanosleep (already in pthread_time.h)
- Add fcntl.h include for _O_BINARY
- Use platform_pipe/fcntl to avoid naming conflicts
- All 22 tests pass on Linux

lib/platform_compat.h

@@ -11,12 +11,15 @@
     #include <windows.h>
     #include <io.h>
     #include <time.h>
+    #include <fcntl.h>
+    #include <stdint.h>
     
     // POSIX functions missing on Windows
     #define strcasecmp _stricmp
     #define strncasecmp _strnicmp
     
-    // poll() implementation for Windows
+    // poll() and pollfd are already defined in winsock2.h on MSYS2 UCRT64
+    // Only define if not already present
     #ifndef POLLIN
         #define POLLIN 0x0001
     #endif
@@ -36,19 +39,9 @@
         #define POLLPRI 0x0002
     #endif
     
-    struct pollfd {
-        int fd;
-        short events;
-        short revents;
-    };
-    
-    // gettimeofday for Windows
-    struct timezone {
-        int tz_minuteswest;
-        int tz_dsttime;
-    };
-    
-    static inline int gettimeofday(struct timeval *tv, struct timezone *tz) {
+    // gettimeofday for Windows (timezone already defined in time.h)
+    #ifndef HAVE_GETTIMEOFDAY
+    static inline int gettimeofday(struct timeval *tv, void *tz) {
         (void)tz;
         if (tv) {
             FILETIME ft;
@@ -62,56 +55,28 @@
         }
         return 0;
     }
+    #endif
     
     // Pipe creation for Windows
-    static inline int pipe(int pipefd[2]) {
+    static inline int platform_pipe(int pipefd[2]) {
         return _pipe(pipefd, 4096, _O_BINARY);
     }
+    #define pipe platform_pipe
     
-    // poll() using select() for Windows
-    static inline int poll(struct pollfd *fds, nfds_t nfds, int timeout) {
-        fd_set readfds, writefds, exceptfds;
-        FD_ZERO(&readfds);
-        FD_ZERO(&writefds);
-        FD_ZERO(&exceptfds);
-        
-        int max_fd = -1;
-        for (nfds_t i = 0; i < nfds; i++) {
-            if (fds[i].fd < 0) continue;
-            if (fds[i].events & POLLIN) FD_SET(fds[i].fd, &readfds);
-            if (fds[i].events & POLLOUT) FD_SET(fds[i].fd, &writefds);
-            FD_SET(fds[i].fd, &exceptfds);
-            if (fds[i].fd > max_fd) max_fd = fds[i].fd;
-        }
-        
-        struct timeval tv, *ptv = NULL;
-        if (timeout >= 0) {
-            tv.tv_sec = timeout / 1000;
-            tv.tv_usec = (timeout % 1000) * 1000;
-            ptv = &tv;
-        }
-        
-        int ret = select(max_fd + 1, &readfds, &writefds, &exceptfds, ptv);
-        if (ret < 0) return ret;
-        
-        // Set revents
-        for (nfds_t i = 0; i < nfds; i++) {
-            fds[i].revents = 0;
-            if (fds[i].fd < 0) continue;
-            if (FD_ISSET(fds[i].fd, &readfds)) fds[i].revents |= POLLIN;
-            if (FD_ISSET(fds[i].fd, &writefds)) fds[i].revents |= POLLOUT;
-            if (FD_ISSET(fds[i].fd, &exceptfds)) fds[i].revents |= POLLERR;
-        }
-        
-        return ret;
-    }
+    // nfds_t already defined in winsock2.h on MSYS2
     
     // fcntl replacement for Windows (simplified - only supports F_GETFL/F_SETFL with O_NONBLOCK)
-    #define F_GETFL 3
-    #define F_SETFL 4
-    #define O_NONBLOCK 0x4000
+    #ifndef F_GETFL
+        #define F_GETFL 3
+    #endif
+    #ifndef F_SETFL
+        #define F_SETFL 4
+    #endif
+    #ifndef O_NONBLOCK
+        #define O_NONBLOCK 0x4000
+    #endif
     
-    static inline int fcntl(int fd, int cmd, ... /* arg */ ) {
+    static inline int platform_fcntl(int fd, int cmd, ... /* arg */ ) {
         va_list ap;
         va_start(ap, cmd);
         
@@ -134,13 +99,9 @@
         errno = EINVAL;
         return -1;
     }
+    #define fcntl platform_fcntl
     
-    // nanosleep replacement
-    static inline int nanosleep(const struct timespec *req, struct timespec *rem) {
-        (void)rem;
-        Sleep((DWORD)(req->tv_sec * 1000 + req->tv_nsec / 1000000));
-        return 0;
-    }
+    // nanosleep already defined in pthread_time.h on MSYS2
     
 #else
     // POSIX - include standard headers