Add "include <stddef.h>" to fts5 and rtree to ensure that they use the

system version of the offsetof() macro when it is available, as the
built-in version triggers ubsan errors with clang.

FossilOrigin-Name: 6ceb1322ef10c1586a7ca97b377dce0c6e35d9abbdbff5a01e841a487eac08cb

ext/fts5/fts5Int.h

@@ -20,6 +20,7 @@ SQLITE_EXTENSION_INIT1
 
 #include <string.h>
 #include <assert.h>
+#include <stddef.h>
 
 #ifndef SQLITE_AMALGAMATION
 

ext/rtree/rtree.c

@@ -64,6 +64,8 @@
 #endif
 int sqlite3GetToken(const unsigned char*,int*); /* In the SQLite core */
 
+#include <stddef.h>
+
 /*
 ** If building separately, we will need some setup that is normally
 ** found in sqliteInt.h