asv config to use `build_ext` instead of `build`
State: closed

Not 100% sure on this change, feel free to close at any time.

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I have not seen a single mention in the docs of ```python setup.py build``` there was only mention of ```python setup.py build_ext```, so I thought that asv should follow that as well (I could be wrong here).


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Comments:
Not sure of the differences between all of these. Is there anything documented in distutils to explain?

FWIW I think the asv command is pulled directly from the ASV docs
@WillAyd I have tried to look for the past hour for the differences, could not find anything that would clarify the differences.

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I did look at the source of each command (```build``` and ```build_ext```) and it looks like ```build``` is also executing the commands ```build_ext``` as well as ```build_py```, ```build_clib``` and ```build_scripts```. I could not understand from the docs/source code what each of them are doing. so maybe better to not touch this one as I don't see a clear difference when using ```build``` over ```build_ext```, one thing I did noticed is that when running ```python setup.py build``` it copies a lot of files from the ```pandas/tests/``` directory into the ```build/``` directory.


Those are just __some__ of the files, there are *many* more.

<details>

```
copying pandas/tests/io/parser/__init__.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/conftest.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_c_parser_only.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_comment.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_common.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_compression.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_converters.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_dialect.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_dtypes.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_encoding.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_header.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_index_col.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_mangle_dupes.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_multi_thread.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_na_values.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_network.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_parse_dates.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_python_parser_only.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_quoting.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_read_fwf.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_skiprows.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_textreader.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_unsupported.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
copying pandas/tests/io/parser/test_usecols.py -> build/lib.linux-x86_64-3.7/pandas/tests/io/parser
```

</details>

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@WillAyd I think you should close this PR, as I can't really tell the difference between the two commands.
Sounds good. If there's no benefit to changing let's just leave for now