nostrdb: add supporting files for the bolt11 parser

A lot of this was pulled from core-lightning. Not sure what is actually
needed or not.

Signed-off-by: William Casarin <jb55@jb55.com>

nostrdb/bolt11/array_size.h

@@ -0,0 +1,26 @@
+/* CC0 (Public domain) - see LICENSE file for details */
+#ifndef CCAN_ARRAY_SIZE_H
+#define CCAN_ARRAY_SIZE_H
+#include "../config.h"
+#include "build_assert.h"
+
+/**
+ * ARRAY_SIZE - get the number of elements in a visible array
+ * @arr: the array whose size you want.
+ *
+ * This does not work on pointers, or arrays declared as [], or
+ * function parameters.  With correct compiler support, such usage
+ * will cause a build error (see build_assert).
+ */
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + _array_size_chk(arr))
+
+#if HAVE_BUILTIN_TYPES_COMPATIBLE_P && HAVE_TYPEOF
+/* Two gcc extensions.
+ * &a[0] degrades to a pointer: a different type from an array */
+#define _array_size_chk(arr)                        \
+    BUILD_ASSERT_OR_ZERO(!__builtin_types_compatible_p(typeof(arr),    \
+                            typeof(&(arr)[0])))
+#else
+#define _array_size_chk(arr) 0
+#endif
+#endif /* CCAN_ALIGNOF_H */