Too many issues will kill our team's development velocity, drastically.
Make sure you have checked all steps below.

### Prerequisite
* [ ] Make sure your problem is not listed in [the common build problems](https://github.com/pyenv/pyenv/wiki/Common-build-problems).
* [ ] Make sure no duplicated issue has already been reported in [the pyenv issues](https://github.com/pyenv/pyenv/issues). You should look for closed issues, too.
* [ ] Make sure you are not asking us to help solving your specific issue.
  * GitHub issues is opened mainly for development purposes. If you want to ask someone to help solving your problem, go to some community site like [Gitter](https://gitter.im/yyuu/pyenv), [StackOverflow](https://stackoverflow.com/questions/tagged/pyenv), etc.
* [ ] Make sure your problem is not derived from packaging (e.g. [Homebrew](https://brew.sh)).
  * Please refer to the package documentation for the installation issues, etc.
* [ ] Make sure your problem is not derived from plugins.
  * This repository is maintaining `pyenv` and the default `python-build` plugin only. Please refrain from reporting issues of other plugins here.

### Description
- [ ] Platform information (e.g. Ubuntu Linux 16.04):
- [ ] OS architecture (e.g. amd64):
- [ ] pyenv version:
- [ ] Python version:
- [ ] C Compiler information (e.g. gcc 7.3): 
- [ ] Please reproduce the problem with debug tracing enabled and attach the resulting output as a gist
  * If the problem happens in a Pyenv invocation, you can turn on tracing by setting `PYENV_DEBUG=1`, e.g. `env PYENV_DEBUG=1 pyenv install -v 3.6.4`
    * If the problem is with `pyenv install`, make sure to also enable its verbose mode (`-v`)
  * If the problem happens outside of a Pyenv invocation, enable shell trace output like this:
     ```sh
     export PS4='+(${(%):-%x}:${LINENO}): ${funcstack[0]:+${funcstack[0]}(): }'  #Zsh
     export PS4='+(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'  #Bash
     set -x
     <reproduce the problem>
     set +x
     ```
