[llvm] MathExtras: rewrite some methods to never overflow (PR #95556)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -385,6 +385,8 @@ inline uint64_t PowerOf2Ceil(uint64_t A) {
 ///   alignTo(~0LL, 8) = 0
 ///   alignTo(321, 255) = 510
 /// \endcode
+///
+/// May overflow.
----------------
artagnon wrote:

Is it okay if I tackle this problem in the next patch (see #95426), since the numbers I need to test with in the current implementation are going to be very big and ugly?


https://github.com/llvm/llvm-project/pull/95556