[RF] Small fixup for using RooFit with new Clad 1.5

Using template functions in the generated code can cause linker errors,
which is avoided with this suggested commit.

To be backported to the 6.32 branch.

roofit/histfactory/src/FlexibleInterpVar.cxx

@@ -241,7 +241,7 @@ void FlexibleInterpVar::translate(RooFit::Detail::CodeSquashContext &ctx) const
    }
 
    std::string const &resName = ctx.buildCall("RooFit::Detail::MathFuncs::flexibleInterp", interpCode,
-                                              _paramList, n, _low, _high, _interpBoundary, _nominal);
+                                              _paramList, n, _low, _high, _interpBoundary, _nominal, 1.0);
    ctx.addResult(this, resName);
 }
 

roofit/histfactory/src/PiecewiseInterpolation.cxx

@@ -239,8 +239,8 @@ void PiecewiseInterpolation::translate(RooFit::Detail::CodeSquashContext &ctx) c
    code += "double * " + highName + " = " + valsHighStr + " + " + nStr + " * " + idxName + ";\n";
    code += "double " + nominalName + " = *(" + valsNominalStr + " + " + idxName + ");\n";
 
-   std::string funcCall = ctx.buildCall("RooFit::Detail::MathFuncs::flexibleInterp<false>", _interpCode[0], _paramSet,
-                                        n, lowName, highName, 1.0, nominalName);
+   std::string funcCall = ctx.buildCall("RooFit::Detail::MathFuncs::flexibleInterp", _interpCode[0], _paramSet, n,
+                                        lowName, highName, 1.0, nominalName, 0.0);
    code += "double " + resName + " = " + funcCall + ";\n";
 
    if (_positiveDefinite)

roofit/roofitcore/inc/RooFit/Detail/MathFuncs.h

@@ -285,16 +285,15 @@ inline double flexibleInterpSingle(unsigned int code, double low, double high, d
    return 0.0;
 }
 
-template <bool cutoff = true>
 inline double flexibleInterp(unsigned int code, double *params, unsigned int n, double *low, double *high,
-                             double boundary, double nominal)
+                             double boundary, double nominal, int doCutoff)
 {
    double total = nominal;
    for (std::size_t i = 0; i < n; ++i) {
       total += flexibleInterpSingle(code, low[i], high[i], boundary, nominal, params[i], total);
    }
 
-   return cutoff && total <= 0 ? TMath::Limits<double>::Min() : total;
+   return doCutoff && total <= 0 ? TMath::Limits<double>::Min() : total;
 }
 
 inline double landau(double x, double mu, double sigma)