Update MathExtras.h

Author: gmh5225

llvm/include/llvm/Support/MathExtras.h

@@ -382,7 +382,10 @@ inline uint64_t alignTo(uint64_t Value, uint64_t Align) {
 inline uint64_t alignToPowerOf2(uint64_t Value, uint64_t Align) {
   assert(Align != 0 && (Align & (Align - 1)) == 0 &&
          "Align must be a power of 2");
-  return (Value + Align - 1) & -Align;
+  // Replace unary minus to avoid compilation error on Windows:
+  // "unary minus operator applied to unsigned type, result still unsigned"
+  uint64_t negAlign = (~Align) + 1;
+  return (Value + Align - 1) & negAlign;
 }
 
 /// If non-zero \p Skew is specified, the return value will be a minimal integer