Fix MKL enum conversion warning.

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### Description
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Fix MKL enum conversion warning.

### Reference issue
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Fixes #2999.

Closes #2999

See merge request libeigen/eigen!2061

Eigen/src/Core/Assign_MKL.h

@@ -56,11 +56,11 @@ class vml_assign_traits {
                                                    : int(Dst::MaxRowsAtCompileTime),
     MaxSizeAtCompileTime = Dst::SizeAtCompileTime,
 
-    MightEnableVml = StorageOrdersAgree && DstHasDirectAccess && SrcHasDirectAccess &&
+    MightEnableVml = bool(StorageOrdersAgree) && bool(DstHasDirectAccess) && bool(SrcHasDirectAccess) &&
                      Src::InnerStrideAtCompileTime == 1 && Dst::InnerStrideAtCompileTime == 1,
-    MightLinearize = MightEnableVml && (int(Dst::Flags) & int(Src::Flags) & LinearAccessBit),
-    VmlSize = MightLinearize ? MaxSizeAtCompileTime : InnerMaxSize,
-    LargeEnough = VmlSize == Dynamic || VmlSize >= EIGEN_MKL_VML_THRESHOLD
+    MightLinearize = bool(MightEnableVml) && (int(Dst::Flags) & int(Src::Flags) & LinearAccessBit),
+    VmlSize = bool(MightLinearize) ? MaxSizeAtCompileTime : InnerMaxSize,
+    LargeEnough = (VmlSize == Dynamic) || VmlSize >= EIGEN_MKL_VML_THRESHOLD
   };
 
  public: