cmake: Custom target for holding properties

Defines an empty custom target whose purpose is to hold properties and configuration
data that can be retrieved using generator expressions in the build phase.

config.cmake

@@ -28,6 +28,8 @@ if(KernelVerificationBuild)
     set(force CLEAR)
 endif()
 mark_as_advanced(${force} CSPEC_DIR SKIP_MODIFIES TOPLEVELTYPES SORRY_BITFIELD_PROOFS UMM_TYPES)
+# Use a custom target for collecting information during generation that we need during build
+add_custom_target(kernel_config_target)
 
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 # Architecture selection