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

[Abhina Sree via llvm-commits]

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@@ -552,6 +552,10 @@ else()
   option(LLVM_ENABLE_THREADS "Use threads if available." ON)
 endif()
 
+set(LLVM_ENABLE_ICU "ON" CACHE STRING "Use ICU for character conversion support if available. Can be ON, OFF, or FORCE_ON")
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abhina-sree wrote:

Can you explain why we should default these to off? And should the default be different for iconv? The original decision in the RFC was to use ICU first if available, then use iconv.

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