Only use general purpose registers in c guest #594

Job	Run time
spell check with typos	3s
docs-pr	4s
fuzzing / fuzz	9m 48s
rust / build (hyperv, amd, debug)	6m 56s
rust / build (hyperv, amd, release)	6m 54s
rust / build (hyperv, intel, debug)	6m 18s
rust / build (hyperv, intel, release)	6m 13s
rust / build (mshv, amd, debug)	6m 49s
rust / build (mshv, amd, release)	6m 31s
rust / build (mshv, intel, debug)	6m 34s
rust / build (mshv, intel, release)	6m 25s
rust / build (mshv3, amd, debug)	7m 43s
rust / build (mshv3, amd, release)	7m 49s
rust / build (mshv3, intel, debug)	7m 34s
rust / build (mshv3, intel, release)	7m 47s
rust / build (kvm, amd, debug)	6m 8s
rust / build (kvm, amd, release)	5m 57s
rust / build (kvm, intel, debug)	6m 38s
rust / build (kvm, intel, release)	6m 27s
	1h 58m 38s

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