libc: Add fileno()

libc/include/stdio.h

@@ -32,6 +32,9 @@ extern "C"
     /* Close a file and frees up its stream. */
     int fclose(FILE* stream);
 
+    /* Return the file descriptor associated with a stream. */
+    int fileno(FILE* stream);
+
     /* Read arbitrarily sized items from a stream. */
     size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream);
 

libc/src/stdio.cpp

@@ -66,6 +66,11 @@ extern "C"
         return 0;
     }
 
+    int fileno(FILE* stream)
+    {
+        return stream->_fd;
+    }
+
     size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream)
     {
         if (size * nmemb == 0) return 0;