#50 Compilation fails with GCC11/std=c++17, duplicate "clamp" definition

[Stefan Brüns]

GCC 11 defaults to C++17, and thus provides std::clamp(T, T, T).

fileformat/pfsinyuv.cpp (re)defines clamp in the global namespace.

As pfsinyuv.cpp has a "using namespace std" from pfsutils.cpp, both definitions clash.

[Stefan Brüns]

The following patch fixes the issue:

[Rafal Mantiuk]

Patched applied and pushed to the master branch. Thanks for the fix.