[libcxx] Reinstate <string.h> and fix overload sets to be const-correct wherever possible

[Duncan P. N. Exon Smith via cfe-commits]

No one is waiting for me on this, are they?  FWIW, this seems like
a good solution to me.  I'll see what I can do internally (I filed
a radar), but other platforms will likely need this anyway.

> On 2016-Jan-08, at 16:06, Richard Smith <richard at metafoo.co.uk> wrote:
> 
> Ping, is this OK to commit?
> 
> On Thu, Dec 10, 2015 at 3:32 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Thu, Dec 10, 2015 at 11:45 AM, Marshall Clow <mclow.lists at gmail.com> wrote:
> On Tue, Dec 8, 2015 at 3:52 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> Ping.
> 
> Sorry about that.
> Completely missed this in my email flood.
> 
> This approach looks ok to me, but I wonder if it would be better to get Apple to fix their iOS C library instead.
> 
> Well, it's not broken in the sense that it does what the C standard library is supposed to do. But it's not providing the "C pieces" of a C++ standard library. I don't know what its design goal is here, but with this patch we don't need to care.
> 
> Duncan offered to file a bug on this, but I don't know if that's happened.
> 
> Are there other broken C libraries that we are concerned with?
> 
> Probably :) I don't know the complete set of C standard library implementations that people use with libc++, but I'd be surprised if Darwin were the only case we need to fix.
>