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

[David Tenty 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.
+if(LLVM_ENABLE_ICU)
+  set(LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
+  set(CMAKE_FIND_LIBRARY_SUFFIXES ".so")
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daltenty wrote:

I checked the AIX ICU libraries, this isn't a concern there as the OS only distributes the shared library version anyway. 

But this check should be generalized to account for the different suffixes on other platforms:
```suggestion
  set(CMAKE_FIND_LIBRARY_SUFFIXES "${CMAKE_SHARED_LIBRARY_SUFFIX}")
```

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