SUMMARY
fails when building:
libs/pigment/compositeops/KoOptimizedCompositeOpFactory.cpp
With error 

In file included from ../libs/pigment/compositeops/KoOptimizedCompositeOpFactory.cpp:20:
In file included from ../libs/pigment/compositeops/KoOptimizedCompositeOpFactoryPerArch.h:24:
In file included from ../libs/pigment/compositeops/KoVcMultiArchBuildSupport.h:39:
In file included from /usr/include/Vc/Vc:30:
In file included from /usr/include/Vc/vector.h:35:
In file included from /usr/include/Vc/avx/vector.h:32:
In file included from /usr/include/Vc/scalar/../common/../avx/casts.h:33:
In file included from /usr/include/Vc/scalar/../common/../avx/../sse/casts.h:31:
/usr/include/Vc/scalar/../common/../sse/intrinsics.h:601:13: error: argument to '__builtin_ia32_vec_ext_v4sf' must be a constant integer
            _MM_EXTRACT_FLOAT(f, v, i);
            ^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/lib/clang/7.0.0/include/smmintrin.h:890:11: note: expanded from macro '_MM_EXTRACT_FLOAT'
  { (D) = __builtin_ia32_vec_ext_v4sf((__v4sf)(__m128)(X), (int)(N)); }
          ^                                                ~~~~~~~~


STEPS TO REPRODUCE
1. Set up compilation with clang and clang++ as compilators
2. Attempt to compile the project

OBSERVED RESULT
The build fails

EXPECTED RESULT
The build succeeds

SOFTWARE VERSIONS
(available in About System)
KDE Plasma Version: 5.12.7
KDE Frameworks Version: 5.47
Qt Version: 5.9.5

ADDITIONAL INFORMATION
LLVM 7 toolchain compiled from source