Initial import of libdpf.

Co-authored-by: Cursor <cursoragent@cursor.com>

thirdparty/hedley/test/returns-non-null.c

@@ -0,0 +1,15 @@
+#include "../hedley.h"
+
+#include <string.h>
+
+static const char* foo = "bar\n";
+
+HEDLEY_RETURNS_NON_NULL
+static const char* get_string(void) {
+  return foo;
+}
+
+int main(void) {
+  const char* s = get_string();
+  return HEDLEY_STATIC_CAST(int, strlen(s));
+}