[llvm] [LLVM] Provide a default 'multilibs.yaml' when configured (PR #192281)

[Petr Hosek via llvm-commits]

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@@ -717,6 +708,56 @@ if(build_runtimes)
           EXTRA_ARGS TARGET_TRIPLE ${name} ${extra_args})
       endforeach()
     endforeach()
+
+    # Generate a default multilib.yaml for each runtime target that has one.
+    if(LLVM_RUNTIME_MULTILIBS)
+      set(_multilib_yaml_outputs)
+      foreach(name ${LLVM_RUNTIME_TARGETS})
+        set(_multilibs_for_target)
+        foreach(multilib ${LLVM_RUNTIME_MULTILIBS})
+          if("${name}" IN_LIST LLVM_RUNTIME_MULTILIB_${multilib}_TARGETS)
+            list(APPEND _multilibs_for_target "${multilib}")
+          endif()
+        endforeach()
+
+        # Generate the file into a temporary. We only copy this if the user has
+        # not provided one either in the build tree or the install directory.
+        if(_multilibs_for_target)
+          set(_yaml "MultilibVersion: 1.0\n\nVariants:\n- Dir: .\n  Flags: []\n")
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petrhosek wrote:

Can you use https://cmake.org/cmake/help/latest/manual/cmake-language.7.html#bracket-argument instead of `\n` to make this more readable?

https://github.com/llvm/llvm-project/pull/192281