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

[Abhina Sree 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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abhina-sree wrote:

This was discussed with the LLVM Board and the summary of their response is on the RFC https://discourse.llvm.org/t/rfc-enabling-fexec-charset-support-to-llvm-and-clang-reposting/71512/30. They wanted an optional dynamic link so there is no impact to LLVM's licence

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