Fix "error: command 'clang' failed with exit status 1"

To fix error: command 'clang' failed with exit status 1 when running `pip install pycurl', install Command Line Tools from Xcode.
- Open Xcode
- Go to Preferences (Command + ,)
- Select the Downloads tab / Components subtab
- Install Command Line Tools
Then pip install with ARCHFLAGS set:
Code
$ env ARCHFLAGS="-arch x86_64" pip install pycurl
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