rcutorture/nolibc: Fix a typo in header file

This fixes a typo. Before this, the AT_FDCWD macro would be defined
regardless of whether or not it's been defined before.
Signed-off-by: NSamuel Hernandez <sam.hernandez.amador@gmail.com>
Signed-off-by: NWilly Tarreau <w@1wt.eu>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/nolibc.h

@@ -231,7 +231,7 @@ struct rusage {
 #define DT_SOCK   12
 
 /* all the *at functions */
-#ifndef AT_FDWCD
+#ifndef AT_FDCWD
 #define AT_FDCWD             -100
 #endif