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
+    BUILD_CFLAGS="$BUILD_CFLAGS -DSQLITE_OMIT_LOAD_EXTENSION=1"
+  fi
 else
   BUILD_CFLAGS="$BUILD_CFLAGS -DSQLITE_OMIT_LOAD_EXTENSION=1"
 fi