all: support linux KCOV_TRACE_UNIQ_[PC|EDGE|CMP] modes #15104

Job	Run time
arch (presubmit_arch_linux)	10m 58s
arch (presubmit_arch_freebsd)	6m 29s
aux	4m 59s
arch (presubmit_arch_netbsd)	4m 22s
dashboard	2m 34s
build	14m 1s
arch (presubmit_arch_openbsd)	4m 17s
gvisor	4m 14s
arch (presubmit_arch_darwin)	4m 18s
old	6m 35s
race	8m 44s
arch (presubmit_arch_windows)	3m 15s
arch (presubmit_arch_executor)	3m 11s
race_dashboard	3m 12s
	1h 21m 9s

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