Attempt to always provide _Thread_local in <sys/reent.h> by including
<sys/cdefs.h>.  The C specific keyword _Thread_local is not available
unless targetting a suitable C version.
---
 newlib/libc/include/sys/reent.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/newlib/libc/include/sys/reent.h b/newlib/libc/include/sys/reent.h
index a6c923f1c..a02e7c2bd 100644
--- a/newlib/libc/include/sys/reent.h
+++ b/newlib/libc/include/sys/reent.h
@@ -12,6 +12,7 @@ extern "C" {
 
 #include <_ansi.h>
 #include <stddef.h>
+#include <sys/cdefs.h>
 #include <sys/_types.h>
 
 #define _NULL 0
-- 
2.34.1