Add feature test macro for fileno()

Defining _POSIX_C_SOURCE is required for POSIX fileno() to become
available.

Signed-off-by: Joseph Schuchart <[email protected]>

Author: devreal

opal/util/keyval/keyval_lex.l

@@ -23,6 +23,9 @@
  * $HEADER$
  */
 
+// needed for fileno()
+#define _POSIX_C_SOURCE 200809L
+
 #include "opal_config.h"
 
 #include <stdio.h>