[Qt-creator] Use #pragma once as default instead of header guards

[Coda Highland]

On Wed, Jan 13, 2016 at 7:52 AM, Joerg Bornemann
<joerg.bornemann at theqtcompany.com> wrote:
> On 13-Jan-16 16:43, Coda Highland wrote:
>
>> #pragma once isn't non-standard. It's defined by the C++11
>> specification and a compliant compiler MUST support it.
>
>
> Can you show me where this is defined?
> AFAICT it is widely supported, but not part of the standard.
>

*opens up working draft* I stand corrected. I had taken a C++ class
that used N3485 as its core textbook, and that class required me to
implement #pragma once. I had misinterpreted this as a requirement of
the specification, but it was actually presented as
implementation-defined and two years later I remembered wrong.

/s/ Adam