[ADT] Simplify IntMask (NFC) (#158410)

We can do the shift in uintptr_t without going through intptr_t.

Author: kazutakahirata

llvm/include/llvm/ADT/PointerIntPair.h

@@ -180,7 +180,7 @@ struct PointerIntPairInfo {
     IntShift = (uintptr_t)PtrTraits::NumLowBitsAvailable - IntBits,
 
     /// IntMask - This is the unshifted mask for valid bits of the int type.
-    IntMask = (uintptr_t)(((intptr_t)1 << IntBits) - 1),
+    IntMask = ((uintptr_t)1 << IntBits) - 1,
 
     // ShiftedIntMask - This is the bits for the integer shifted in place.
     ShiftedIntMask = (uintptr_t)(IntMask << IntShift)