[software] Disable LLVM compilation #1116

Job	Run time
check-opcodes	3s
riscv-isa-sim	21s
tc-gcc	2m 8s
tc-llvm	4m 16s
verilator	19s
verilator-model (minpool)	3m 41s
verilator-model (mempool)	17m 56s
check-bootrom	20s
build-apps-omp (minpool)	52s
build-apps-gcc (minpool)	1m 9s
build-apps-gcc (mempool)	1m 23s
build-apps-omp (mempool)	47s
tc-halide	22s
build-apps-llvm (minpool)	1m 51s
build-apps-llvm (mempool)	1m 24s
build-apps-halide (minpool)	1m 22s
build-apps-halide (mempool)	1m 9s
run-apps-halide (minpool)	36s
unit-test	1m 43s
run-apps-halide (mempool)	2m 58s
run-apps-gcc (minpool)	42s
run-apps-llvm (minpool)	34s
run-apps-gcc (mempool)	4m 23s
run-apps-llvm (mempool)	2m 55s
clean-up	4s
clean-up-compile-runs (minpool)	5s
clean-up-compile-runs (mempool)	5s
	53m 28s

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