[clang] [compiler-rt] [llvm] Reapply "Skipping host target exports during cross-compilation" (#210… (PR #210496)

[Petr Hosek via cfe-commits]

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@@ -76,6 +76,16 @@ if(LLVM_BINARY_DIR)
   list(APPEND llvm_search_paths "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm")
   list(APPEND clang_search_paths "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/clang")
 endif()
+
+# Exports from LLVM and Clang may contain shared libraries. When targeting
+# baremetal platforms that lacks shared library support, importing such
+# exports unrestrictedly will trigger cmake errors. Set
+# LLVM_OMIT_EXPORTS_FROM_CONFIG flag to skip importing these exports.
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petrhosek wrote:

```suggestion
# Exports from LLVM and Clang may contain shared libraries. When targeting
# platforms that lack shared library support, importing such
# exports unrestrictedly will trigger an error. Set
# LLVM_OMIT_EXPORTS_FROM_CONFIG flag to skip importing these exports.
```

https://github.com/llvm/llvm-project/pull/210496