When I build 3.70.b5 in Mac , the compiler raise an error show that 

"./Modules/posixmodule.c:6018:11: error: implicit declaration of function 'forkpty' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    pid = forkpty(&master_fd, NULL, NULL, NULL);"

the makefile was generated by './configuration" command without no argument.

Have you run "xcode-select --install" to ensure system header files are installed?  If so, what compiler are you using from what source?  What version of macOS are you using?

https://devguide.python.org/setup/#macos

Sure, I already set "xcode-select --install" in terminal

Python 3.6.5 build success with a default setting when running ./configuration" command

Xcode version is 9.3

System version 10.13.4

Sorry, I can't reproduce it and I do not recall every seeing a failure like that.

Just to be sure, you do mean ".configure" and not "./configuration"?

Perhaps you are picking up an old, third-party version of libutil from /usr/local/lib and/or /usr/local/include?  You have tried building from a clean directory?  It looks like the library is searched for at the following section of configure.ac (which is used to generate configure):

https://github.com/python/cpython/blob/v3.7.0b5/configure.ac#L3772

Actually, I found some interesting problem.

In Python 3.6.5 has declared the `extern pid_t forkpty(int *, char *, struct termios *, struct winsize *);`  in here https://github.com/python/cpython/blob/3.6/Include/pyport.h#L532

and I add it into the Python 3.7.0b5's pyport.h, It builds success!

That change should not have affected the macOS build.  Now that you have a working python, can you please run:

./python.exe -m test.pythoninfo

and report the results here?

The result in here 

https://gist.github.com/Zheaoli/86b04395748b998ad7d870a927a95aea

The only really suspicious thing I see is that your shell PATH is *gigantic*. pulling things in from all over the place including Homebrew.  If you want to pursue further, suggest you try a clean build from the tarball without the modification and use a simple PATH like:

export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

I'm willing to bet that some old versions of headers and/or libs are being picked up somewhere.  You probably should go through and permanently clean up that PATH.  Also make sure your Homebrew installation is up-to-date.  Rather than pulling in things from various places, consider pulling everything you need from Homebrew; it looks like you may have run various binary installers of various things in the past.  I'm going to close this issue.  Feel free to re-open if you discover something that appears to be a bug in Python.  Good luck!

it seems like what you say

but I think that you can't ensure everyone has a clean path especially when people use some tools such as pyenv or others to build Python from source code, but not get the binary package directly.

Anyway, it's just a personal idea. Thanks for what you do.

As I said, I do not recall ever seeing a failure like this before and I regularly build and test Python on macOS in many different versions and environments.  It would be very time-consuming to try to debug your environment remotely, time that would be better spent on other problems, I'm afraid.  If you can demonstrate that the problem is with a clean version of pyenv, for example, then that's something to pursue with the pyenv project or here.  But, as it stands, there are so many ways things could have gone wrong for you that it would be foolish for me to try to guess.  Sorry!

Finally, I must say when I first build the Python 3.7.0b5, I don't use Pyenv or others tools.

As you say, It should be a PATH problem. I build success without no patch in a  clean Mac. I think I will figure out what's wrong.

But just as what I say, You can't ensure everyone has a clean PATH.

Anyway, Thanks for your helping!