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

[Abhina Sree via llvm-commits]

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@@ -572,6 +572,10 @@ else()
   option(LLVM_ENABLE_THREADS "Use threads if available." ON)
 endif()
 
+set(LLVM_ENABLE_ICU "OFF" CACHE STRING "Use ICU for character conversion support if available. Can be ON, OFF, or FORCE_ON")
+
+set(LLVM_ENABLE_ICONV "OFF" CACHE STRING "Use iconv for character conversion support if available. Can be ON, OFF, or FORCE_ON")
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abhina-sree wrote:

I think the community preferred ICU over iconv, so it would make more sense to enable ICU and disable iconv, or disable both as the default

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