tools/syz-declextract: improve declaration name extraction #14380

Job	Run time
build	7m 22s
aux	4m 42s
dashboard	3m 5s
arch (presubmit_arch_linux)	10m 33s
arch (presubmit_arch_freebsd)	6m 28s
gvisor	4m 11s
old	6m 31s
arch (presubmit_arch_netbsd)	4m 20s
race	7m 21s
arch (presubmit_arch_openbsd)	4m 15s
race_dashboard	3m 17s
arch (presubmit_arch_darwin)	4m 12s
arch (presubmit_arch_windows)	3m 22s
arch (presubmit_arch_executor)	3m 16s
	1h 12m 55s

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