[llvm] [mlir] Config: Move LLVM_HAS_*_TARGET definitions to a new header. (PR #136388)

[Peter Collingbourne via llvm-commits]

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@@ -384,6 +387,12 @@ write_cmake_config("llvm-config") {
   } else {
     values += [ "LLVM_FORCE_ENABLE_STATS=" ]
   }
+}
+
+write_cmake_config("Targets") {
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pcc wrote:

@nico @aeubanks Alternatively we could just remove this build target; nothing that GN is currently capable of building needs it.

https://github.com/llvm/llvm-project/pull/136388