[libclc] [libclc] Give a helpful error when an unknown target is requested (PR #111528)

[David Spickett via cfe-commits]

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@@ -151,6 +147,17 @@ if( "spirv-mesa3d-" IN_LIST LIBCLC_TARGETS_TO_BUILD OR "spirv64-mesa3d-" IN_LIST
   endif()
 endif()
 
+if( LIBCLC_TARGETS_TO_BUILD STREQUAL "all" )
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DavidSpickett wrote:

I've put this after the spir-v tool check so that if you already knew to ask for `spirv-mesa3d-`, you will still get an error if the tool is not installed. Instead of getting "unknown target spirv-mesa3d-".

https://github.com/llvm/llvm-project/pull/111528