[llvm] ADT: Add constructor from uint64_t array for Bitset (PR #162703)

[Jakub Kuderski via llvm-commits]

================
@@ -45,7 +45,18 @@ class Bitset {
   StorageType Bits{};
 
 protected:
-  constexpr Bitset(const StorageType &B) : Bits{B} {}
+  constexpr Bitset(const std::array<uint64_t, (NumBits + 63) / 64> &B) {
+    if (sizeof(BitWord) == sizeof(uint64_t)) {
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kuhar wrote:

```suggestion
    if constexpr (sizeof(BitWord) == sizeof(uint64_t)) {
```

https://github.com/llvm/llvm-project/pull/162703