libc++ PATCH - partial implementation of LWG 2350 - min, max, and minmax should be constexpr

[Ahmed Charles]

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> From: mclow.lists at gmail.com
> Subject: libc++ PATCH - partial implementation of LWG 2350 - min, max, and minmax should be constexpr
> Date: Tue, 18 Feb 2014 13:35:15 -0800
> To: cfe-commits at cs.uiuc.edu
> 
> Implements for min/max, and some of the minmax specializations.
> In particular, the minmax(initializer_list) is not complete.
> 
> http://cplusplus.github.io/LWG/lwg-active.html#2350

Mostly style things:

1. Some lines introduce tabs and I'm not sure if that's intentional.
2. Some function calls and static_assert's have spaces like 'static_assert (' and 'max (' and some are like 'static_assert(' and 'max('. Is that intentional?

Other than that, LGTM.