[llvm] [LLVM][runtimes] Prepopulate `LLVM_BUILTIN_TARGETS` with runtimes values (PR #95554)

[Chris B via llvm-commits]

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@@ -138,37 +142,44 @@ endfunction()
 # before the just-built compiler can pass the configuration tests.
 get_compiler_rt_path(compiler_rt_path)
 if(compiler_rt_path)
-  if(NOT LLVM_BUILTIN_TARGETS)
+  # If the user did not specify the targets infer them from the runtimes.
+  set(builtin_targets ${LLVM_BUILTIN_TARGETS})
+  if(NOT builtin_targets)
+    if("compiler-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
+      list(APPEND builtin_targets "default")
+    endif()
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llvm-beanz wrote:

The "default" target is also important for how the compiler-rt parts of this are built on Darwin, which is a mess.

https://github.com/llvm/llvm-project/pull/95554