libc: Implement fileno()

libs/libc/include/stdio.h

@@ -40,6 +40,9 @@ extern "C"
     /* Returns a new file associated with the file descriptor fd. */
     FILE* fdopen(int fd, const char* mode);
 
+    /* Returns the file descriptor associated with the file stream. */
+    int fileno(FILE* stream);
+
     /* Writes formatted output according to the string format to the file stream. */
     int fprintf(FILE* stream, const char* format, ...);
 

libs/libc/src/file.cpp

@@ -53,6 +53,11 @@ extern "C"
         return stream;
     }
 
+    int fileno(FILE* stream)
+    {
+        return stream->f_fd;
+    }
+
     size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream)
     {
         ssize_t status = read(stream->f_fd, buf, size * nmemb);