vm: fix lddw helper definition bug of `llvm-jit` #217

Job	Run time
build-runtime	6m 34s
build-and-test (libbpf-tools/opensnoop, ./opensnoop, ./victim, true, 0 test.txt)	1m 3s
build-and-test (libbpf-tools/statsnoop, ./statsnoop, ./victim, true, victim 0 0 ...	1m 15s
build-and-test (malloc, ./malloc, ./victim, false, malloc calls: )	47s
build-and-test (opensnoop, ./opensnoop, ./victim, true, 0 test.txt)	1m 8s
build-and-test (sslsniff, ./sslsniff, /bin/wget https://www.google.com, false, ----- DATA -----)	59s
build-and-test (libbpf-tools/bashreadline, ./readline, /bin/bash, false, info)	48s
	12m 34s

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