Disambiguate clamp calls in exrToDpx.cpp

[carlocab]

C++17 now has std::clamp¹, so the calls to clamp in this file
cause the compiler to error with²

  /tmp/ctl-20240930-89937-yvomao/CTL-ctl-1.5.3/OpenEXR_CTL/exrdpx/exrToDpx.cpp:172:19: error: call to 'clamp' is ambiguous
    172 |                 (unsigned int) (clamp (float (pixel.r), 0.0f, 1023.0f) + 0.5f);
        |                                 ^~~~~
  /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/c++/v1/__algorithm/clamp.h:35:1: note: candidate function [with _Tp = float]
     35 | clamp(_LIBCPP_LIFETIMEBOUND const _Tp& __v,
        | ^
  /opt/homebrew/include/Imath/ImathFun.h:77:1: note: candidate function [with T = float]
     77 | clamp (T a, T l, T h) IMATH_NOEXCEPT
        | ^
  /tmp/ctl-20240930-89937-yvomao/CTL-ctl-1.5.3/OpenEXR_CTL/exrdpx/exrToDpx.cpp:175:19: error: call to 'clamp' is ambiguous
    175 |                 (unsigned int) (clamp (float (pixel.g), 0.0f, 1023.0f) + 0.5f);
        |                                 ^~~~~
  /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/c++/v1/__algorithm/clamp.h:35:1: note: candidate function [with _Tp = float]
     35 | clamp(_LIBCPP_LIFETIMEBOUND const _Tp& __v,
        | ^
  /opt/homebrew/include/Imath/ImathFun.h:77:1: note: candidate function [with T = float]
     77 | clamp (T a, T l, T h) IMATH_NOEXCEPT
        | ^
  /tmp/ctl-20240930-89937-yvomao/CTL-ctl-1.5.3/OpenEXR_CTL/exrdpx/exrToDpx.cpp:178:19: error: call to 'clamp' is ambiguous
    178 |                 (unsigned int) (clamp (float (pixel.b), 0.0f, 1023.0f) + 0.5f);
        |                                 ^~~~~
  /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include/c++/v1/__algorithm/clamp.h:35:1: note: candidate function [with _Tp = float]
     35 | clamp(_LIBCPP_LIFETIMEBOUND const _Tp& __v,
        | ^
  /opt/homebrew/include/Imath/ImathFun.h:77:1: note: candidate function [with T = float]
     77 | clamp (T a, T l, T h) IMATH_NOEXCEPT
        | ^
  3 errors generated.
  make[2]: *** [OpenEXR_CTL/exrdpx/CMakeFiles/exrdpx.dir/exrToDpx.cpp.o] Error 1

Both this code and Imath::clamp long predate std::clamp, so it seems
to me that Imath::clamp is what's intended here.

This fixes a build failure at Homebrew while rebuilding CTL for OpenEXR
3.3.0.³

Footnotes

1. https://en.cppreference.com/w/cpp/algorithm/clamp ↩

2. Logs available at https://github.com/Homebrew/homebrew-core/actions/runs/11113893071/job/30879442929?pr=192399#step:3:375 ↩

3. See https://github.com/Homebrew/homebrew-core/pull/192399 ↩

[michaeldsmith]

thanks for the contribution!

[carlocab]

Thanks for the quick review!