Use std::isnan instead of isnan (#39266)

Author: Pasarus

Framework/DataObjects/inc/MantidDataObjects/VectorColumn.h

@@ -131,7 +131,7 @@ template <class Type> class MANTID_DATAOBJECTS_DLL VectorColumn : public API::Co
       for (size_t j = 0; j < m_data[i].size(); j++) {
         double const left = static_cast<double>(m_data[i][j]);
         double const right = static_cast<double>(otherData[i][j]);
-        if (nanEqual && std::isnan(left) && isnan(right)) {
+        if (nanEqual && std::isnan(left) && std::isnan(right)) {
           continue;
         } else if (!Kernel::withinAbsoluteDifference(left, right, tolerance)) {
           return false;
@@ -154,7 +154,7 @@ template <class Type> class MANTID_DATAOBJECTS_DLL VectorColumn : public API::Co
       for (size_t j = 0; j < m_data[i].size(); j++) {
         double const left = static_cast<double>(m_data[i][j]);
         double const right = static_cast<double>(otherData[i][j]);
-        if (nanEqual && std::isnan(left) && isnan(right)) {
+        if (nanEqual && std::isnan(left) && std::isnan(right)) {
           continue;
         } else if (!Kernel::withinRelativeDifference(left, right, tolerance)) {
           return false;

Framework/Kernel/src/FloatingPointComparison.cpp

@@ -214,7 +214,7 @@ inline bool withinRelativeDifference(T const x, T const y, S const tolerance, MA
   // handles the case of infinities
   if (std::isinf(x) && std::isinf(y))
     // if both are +inf, return true; if both -inf, return true; else false
-    return isnan(static_cast<S>(x - y));
+    return std::isnan(static_cast<S>(x - y));
   S const num = static_cast<S>(absoluteDifference<T>(x, y));
   if (num <= std::numeric_limits<S>::epsilon()) {
     // if |x-y| == 0.0 (within machine tolerance), this test passes