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

[Hubert Tong via llvm-commits]

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@@ -294,6 +294,41 @@ if(LLVM_HAS_LOGF128)
   set(LLVM_HAS_LOGF128 "${HAS_LOGF128}")
 endif()
 
+if (LLVM_ENABLE_ICU STREQUAL FORCE_ON AND LLVM_ENABLE_ICONV STREQUAL FORCE_ON)
+  message(FATAL_ERROR "Both LLVM_ENABLE_ICU and LLVM_ENABLE_ICONV should not be FORCE_ON")
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hubert-reinterpretcast wrote:

The placement of "both" matters for parsing the sentence:
"both not be" (current version) => !X && !Y
"not both be" (suggested version) => !(X && Y)


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