Fix non-OpenMP build

rtengine/imagefloat.cc

@@ -108,8 +108,6 @@ void Imagefloat::setScanline (int row, unsigned char* buffer, int bps, unsigned
 }
 
 
-namespace rtengine { extern void filmlike_clip(float *r, float *g, float *b); }
-
 void Imagefloat::getScanline (int row, unsigned char* buffer, int bps, bool isFloat) const
 {
 
@@ -441,11 +439,15 @@ void Imagefloat::calcCroppedHistogram(const ProcParams &params, float scale, LUT
     int x1, x2, y1, y2;
     params.crop.mapToResized(width, height, scale, x1, x2, y1, y2);
 
+#ifdef _OPENMP
     #pragma omp parallel
+#endif
     {
         LUTu histThr(65536);
         histThr.clear();
+#ifdef _OPENMP
         #pragma omp for nowait
+#endif
 
         for (int y = y1; y < y2; y++) {
             for (int x = x1; x < x2; x++) {
@@ -461,7 +463,9 @@ void Imagefloat::calcCroppedHistogram(const ProcParams &params, float scale, LUT
             }
         }
 
+#ifdef _OPENMP
         #pragma omp critical
+#endif
         {
             for(int i = 0; i <= 0xffff; i++) {
                 hist[i] += histThr[i];