Fix installation of pthash.

[vegetableysm]

What do these changes do?

As tittled.

Example: test.cc

#include <memory>
#include <set>
#include <string.h>
#include <string_view>
#include "grape/utils/pthash_utils/single_phf_view.h"

using namespace grape;

int main() {
  return 0;
}

CMakelists.txt

cmake_minimum_required(VERSION 3.26)
project(test1)
add_executable(test test.cc)
find_package(libgrapelite REQUIRED)
target_include_directories(test PUBLIC ${LIBGRAPELITE_INCLUDE_DIRS})

Shell

cmake .
make

It triggers an error:

The reason of this fault is that currently grape will not install the pthash header to /usr/local/include.