Fix building with dlopen() not available.

--- configure.ac
+++ configure.ac
@@ -102,6 +102,9 @@
   [], [enable_dynamic_extensions=yes])
 if test x"$enable_dynamic_extensions" != "xno"; then
   AC_SEARCH_LIBS(dlopen, dl)
+  if test "${ac_cv_search_dlopen}" = "no" ; then
+    DYNAMIC_EXTENSION_FLAGS=-DSQLITE_OMIT_LOAD_EXTENSION=1
+  fi
 else
   DYNAMIC_EXTENSION_FLAGS=-DSQLITE_OMIT_LOAD_EXTENSION=1
 fi