Make sure we don't user std{err,in,out} if they don't exist.

This is required for target build in libosmocore

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/src/process.c b/src/process.c
index ab4b37e..180efa5 100644
--- a/src/process.c
+++ b/src/process.c
@@ -63,9 +63,12 @@
 		return rc;
 
 	/* Redirect stdio to /dev/null */
+/* since C89/C99 says stderr is a macro, we can safely do this! */
+#ifdef stderr
 	freopen("/dev/null", "r", stdin);
 	freopen("/dev/null", "w", stdout);
 	freopen("/dev/null", "w", stderr);
+#endif
 
 	return 0;
 }