fix(llvm_backend): correct basic value handling and add unimplemented… #9

Job	Run time
runtime smoke	42s
SIMD contract (Cranelift)	41s
parse conformance	41s
fmt + clippy	12s
type + lowering conformance	45s
backend features (llvm-backend)	1m 22s
backend features (default)	52s
	5m 15s

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