Add missing #include for definition.

src/slurmd/slurmd/xcpu.c

@@ -33,6 +33,7 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <signal.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>