[libc] [llvm] [libc][NFC] Remove __support/bit.h and use __support/CPP/bit.h instead (PR #73939)

[Guillaume Chatelet via llvm-commits]

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@@ -152,9 +152,9 @@ class HashState {
     }
   }
   LIBC_INLINE uint64_t finish() {
-    uint64_t rot = buffer & 63;
+    int rot = buffer & 63;
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gchatelet wrote:

I think this doesn't work. I believe we're in [this case](https://en.cppreference.com/w/c/language/conversion#:~:text=otherwise%2C%20if%20the%20target%20type%20is%20signed%2C%20the%20behavior%20is%20implementation%2Ddefined%20(which%20may%20include%20raising%20a%20signal)) : _Integer conversions : if the target type is signed, the behavior is implementation-defined (which may include raising a signal)_.

I changed the code to fall in [this case](https://en.cppreference.com/w/c/language/conversion#:~:text=if%20the%20target%20type%20can%20represent%20the%20value%2C%20the%20value%20is%20unchanged) : _if the target type can represent the value, the value is unchanged_.

https://github.com/llvm/llvm-project/pull/73939