[llvm] Fix warnings while building llvm against emscripten for web assembly (PR #118262)

[Sam Clegg via llvm-commits]

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@@ -635,6 +635,11 @@ function(llvm_add_library name)
     set(ARG_STATIC)
   endif()
 
+  if(EMSCRIPTEN)
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sbc100 wrote:

Perhaps add `set(ARG_STATIC)` too?

Perhaps add a comment here:  "Emscripten's support for dynamic linking is limited so force all libraries to be statically linked"

https://github.com/llvm/llvm-project/pull/118262