keep workaround for the intended compiler only

Author: sloriot

QP_solver/include/CGAL/QP_solver/functors.h

@@ -254,6 +254,7 @@ class Map_with_default {
     : map(m), d(v)
   {}
 
+#if defined(BOOST_MSVC) && (_MSC_VER < 1920) // 1920 is Visual Studio 2019 version 16.0.0
   // Added as workaround for VC2017 with /arch:AVX to fix
   // https://cgal.geometryfactory.com/CGAL/testsuite/CGAL-4.14-I-95/QP_solver/TestReport_afabri_x64_Cygwin-Windows10_MSVC2017-Release-64bits.gz
   Map_with_default& operator=(const Map_with_default& other)
@@ -262,6 +263,7 @@ class Map_with_default {
     d = other.d;
     return *this;
   }
+#endif
 
   // operator()
   const mapped_type& operator() (key_type n) const {