Cannot Find hphp/util/hphp-config.h when compile a hhvm extension

### HHVM Version
hello，when I setup hhvm，and try to compile a offical extension example,I have a issue
In file included from /usr/include/hphp/runtime/base/string-data.h:24:0,
from /usr/include/hphp/runtime/base/type-string.h:22,
from /usr/include/hphp/runtime/base/debuggable.h:19,
from /usr/include/hphp/runtime/ext/extension.h:21,
from /root/extension-example/example.cpp:17:
/usr/include/hphp/util/hash.h:26:37: fatal error: hphp/util/hphp-config.h: No such file or directory
compilation terminated.
CMakeFiles/example.dir/build.make:62: recipe for target 'CMakeFiles/example.dir/example.cpp.o' failed
make[2]: *** [CMakeFiles/example.dir/example.cpp.o] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/example.dir/all' failed
make[1]: *** [CMakeFiles/example.dir/all] Error 2
Makefile:127: recipe for target 'all' failed
make: *** [all] Error 2
my hhvm version is:
root@ubuntu:~/extension-example# hhvm --version
HipHop VM 3.26.3 (rel)
Compiler: 1527193322_776794697
Repo schema: 70d14a0c2b5b8c1c820c09f57b1825a5081867cb
root@ubuntu:~/extension-example# hh_client --version
hh-b018e564c11827a6aca2edf495e909a17e2b85e5-3.26.3 Thu May 24 13:23:52 2018
Can you help me?