[Bitstream] Use alignTo to make code more readable. NFC

I was recently debugging a similar issue to https://reviews.llvm.org/D86500 only with a large metadata section. Only after I finished debugging it did I discover it was fixed very recently.

My version of the fix was going to alignTo since that uses uint64_t and improves the readability of the code. So I though I would go ahead and share it.

Differential Revision: https://reviews.llvm.org/D86957

llvm/lib/Bitstream/Reader/BitstreamReader.cpp

@@ -187,8 +187,7 @@ Expected<unsigned> BitstreamCursor::skipRecord(unsigned AbbrevID) {
     SkipToFourByteBoundary();  // 32-bit alignment
 
     // Figure out where the end of this blob will be including tail padding.
-    const size_t NewEnd =
-        GetCurrentBitNo() + ((static_cast<uint64_t>(NumElts) + 3) & ~3) * 8;
+    const size_t NewEnd = GetCurrentBitNo() + alignTo(NumElts, 4) * 8;
 
     // If this would read off the end of the bitcode file, just set the
     // record to empty and return.
@@ -316,8 +315,7 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
 
     // Figure out where the end of this blob will be including tail padding.
     size_t CurBitPos = GetCurrentBitNo();
-    const size_t NewEnd =
-        CurBitPos + ((static_cast<uint64_t>(NumElts) + 3) & ~3) * 8;
+    const size_t NewEnd = CurBitPos + alignTo(NumElts, 4) * 8;
 
     // If this would read off the end of the bitcode file, just set the
     // record to empty and return.