clean build warnings

Chapter07/error_handling/cstdlib_support/nosys_stubs.c

@@ -0,0 +1,21 @@
+#include <sys/stat.h>
+#include <errno.h>
+#include <_ansi.h>
+#include <reent.h>
+
+/* Minimal implementation of _fstat_r */
+int _fstat_r(struct _reent *r, int file, struct stat *st) {
+    st->st_mode = S_IFCHR; /* Character device */
+    return 0;
+}
+
+/* Minimal implementation of _getpid_r */
+int _getpid_r(struct _reent *r) {
+    return 1; /* Return a dummy process ID */
+}
+
+/* Minimal implementation of _kill_r */
+int _kill_r(struct _reent *r, int pid, int sig) {
+    r->_errno = EINVAL;
+    return -1; /* Indicate failure */
+}