assorted syz-declextract improvments #14388

Job	Run time
build	1m 14s
arch (presubmit_arch_linux)	1m 30s
aux	1m 31s
dashboard	1m 11s
arch (presubmit_arch_freebsd)	1m 31s
arch (presubmit_arch_netbsd)	1m 31s
gvisor	1m 31s
old	1m 33s
arch (presubmit_arch_openbsd)	1m 30s
race	1m 13s
arch (presubmit_arch_darwin)	1m 31s
race_dashboard	1m 10s
arch (presubmit_arch_windows)	1m 31s
arch (presubmit_arch_executor)	1m 29s
	19m 56s

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