basic: add STRERROR() wrapper for strerror_r()

src/basic/errno-util.h

@@ -6,6 +6,16 @@
 
 #include "macro.h"
 
+/* strerror(3) says that glibc uses a maximum length of 1024 bytes. */
+#define ERRNO_BUF_LEN 1024
+
+/* Note: the lifetime of the compound literal is the immediately surrounding block,
+ * see C11 §6.5.2.5, and
+ * https://stackoverflow.com/questions/34880638/compound-literal-lifetime-and-if-blocks
+ *
+ * Note that we use the GNU variant of strerror_r() here. */
+#define STRERROR(errnum) strerror_r(abs(errnum), (char[ERRNO_BUF_LEN]){}, ERRNO_BUF_LEN)
+
 static inline void _reset_errno_(int *saved_errno) {
         if (*saved_errno < 0) /* Invalidated by UNPROTECT_ERRNO? */
                 return;