mac OS X 10.15.x pyenv Python インストールできない場合

## pyenv でのpython インストールに失敗してしまう場合
こんな風に
Catalina のベータ版で起きやすいようです

```
% pyenv install 3.8.0
python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.8.0.tar.xz...
-> https://www.python.org/ftp/python/3.8.0/Python-3.8.0.tar.xz
Installing Python-3.8.0...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 10.15.3 using python-build 1.2.15-9-gac246e16)

Inspect or clean up the working tree at /var/folders/xm/g1kzbj4504vc7jy43b8jls480000gn/T/python-build.20191222050242.8852
Results logged to /var/folders/xm/g1kzbj4504vc7jy43b8jls480000gn/T/python-build.20191222050242.8852.log

Last 10 log lines:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread.h:540:6: warning: macro expansion producing 'defined' has undefined behavior [-Wexpansion-to-defined]
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread.h:200:34: note: expanded from macro '_PTHREAD_SWIFT_IMPORTER_NULLABILITY_COMPAT'
        defined(SWIFT_CLASS_EXTRA) && (!defined(SWIFT_SDK_OVERLAY_PTHREAD_EPOCH) || (SWIFT_SDK_OVERLAY_PTHREAD_EPOCH < 1))
                                        ^
220 warnings and 10 errors generated.
make: *** [Parser/parser.o] Error 1
220 warnings and 10 errors generated.
make: *** [Parser/bitset.o] Error 1
220 warnings and 10 errors generated.
make: *** [Parser/metagrammar.o] Error 1

```

## pyenv を再インストール
```
% mv .pyenv .pyenv_old
% git clone git://github.com/yyuu/pyenv.git ~/.pyenv
Cloning into '/Users/xxx/.pyenv'...
remote: Enumerating objects: 26, done.
remote: Counting objects: 100% (26/26), done.
remote: Compressing objects: 100% (20/20), done.
remote: Total 17572 (delta 9), reused 9 (delta 3), pack-reused 17546
Receiving objects: 100% (17572/17572), 3.44 MiB | 3.90 MiB/s, done.
Resolving deltas: 100% (11936/11936), done.

% echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bash_profile
% echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile
% echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
% source .bash_profile 
```

## 環境整備
```
% brew install readline xz openssl zlib
```

## インストール実行

```
% env SDKROOT="/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk" CFLAGS="-I/usr/local/opt/openssl/include -I/usr/local/opt/readline/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include" CPPFLAGS="-I/usr/local/opt/zlib/include" LDFLAGS="-L/usr/local/opt/openssl/lib -L/usr/local/opt/readline/lib" pyenv install 3.8.0
python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.8.0.tar.xz...
-> https://www.python.org/ftp/python/3.8.0/Python-3.8.0.tar.xz
Installing Python-3.8.0...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk
Installed Python-3.8.0 to /Users/xxx/.pyenv/versions/3.8.0

% pyenv global 3.8.0
```

初回のインストール時にこれが必要っぽい

```
SDKROOT="/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk"

CFLAGS="-I/usr/local/opt/openssl/include -I/usr/local/opt/readline/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include" 

CPPFLAGS="-I/usr/local/opt/zlib/include"

LDFLAGS="-L/usr/local/opt/openssl/lib -L/usr/local/opt/readline/lib"
```