Fail codegen example configuration if no dependcies

We rather want to fail CMake configuration than silently move on,
to find out about missing example, after the build. Codegen example
is only build "on demand", when UR_BUILD_EXAMPLE_CODEGEN is set.

Author: lukaszstolarczuk

examples/codegen/CMakeLists.txt

@@ -43,5 +43,5 @@ if(LLVM_FOUND AND PkgConfig_FOUND AND LLVMSPIRVLib_FOUND)
         )
     endif()
 else()
-    message(STATUS "The environment did not satisfy dependency requirements (LLVM, PkgConfig, LLVMSPIRVLib) for codegen example (skipping target).")
+    message(FATAL_ERROR "The environment did not satisfy dependency requirements (LLVM, PkgConfig, LLVMSPIRVLib) for codegen example (skipping target).")
 endif()