[llvm] Create a CharSetConverter class with both iconv and icu support (PR #74516)

[Hubert Tong via llvm-commits]

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@@ -294,6 +294,37 @@ if(LLVM_HAS_LOGF128)
   set(LLVM_HAS_LOGF128 "${HAS_LOGF128}")
 endif()
 
+# Check for ICU.
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hubert-reinterpretcast wrote:

Can you please add this into the code comments. Otherwise, it is likely some PR is going to show up to change this and the rationale would have been lost.

https://github.com/llvm/llvm-project/pull/74516