[llvm] Make more math&bit functions constexpr, NFC (PR #145856)

[Jakub Kuderski via llvm-commits]

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@@ -200,7 +200,7 @@ template <typename T> [[nodiscard]] int countr_zero(T Val) {
 /// Only unsigned integral types are allowed.
 ///
 /// Returns std::numeric_limits<T>::digits on an input of 0.
-template <typename T> [[nodiscard]] int countl_zero(T Val) {
+template <typename T> [[nodiscard]] constexpr int countl_zero(T Val) {
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kuhar wrote:

+1, this could be unit-tested

https://github.com/llvm/llvm-project/pull/145856