[libclc] [llvm] [libclc] Support LLVM_ENABLE_RUNTIMES when building (PR #141574)

[Fraser Cormack via llvm-commits]

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@@ -204,6 +204,13 @@ if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
   endif ()
 endif ()
 
+if ("libclc" IN_LIST LLVM_ENABLE_PROJECTS)
+  message(WARNING "Using LLVM_ENABLE_PROJECTS=libclc is deprecated now, and will "
+    "become a fatal error in the LLVM 21 release.  Please use "
+    "-DLLVM_ENABLE_RUNTIMES=libclc or see the instructions at "
+    "https://libclc.llvm.org/ for building the runtimes.")
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frasercrmck wrote:

Yes the message to refer to the URL is misleading, sorry. Though the first part - `-DLLVM_ENABLE_RUNTIMES=libclc` - should be enough to build libclc. It should just be switching from `PROJECTS` to `RUNTIMES`.

https://github.com/llvm/llvm-project/pull/141574