CMake+Rust: Fix offline builds w. vendored git repos #2007

Job	Run time
check (libclamav, (iana_cctld\|bytecode_api_\|bytecode_hooks\|rijndael\|yara\|inffixed\|inflate\|queue\|n...	21s
check (libfreshclam)	19s
check (clamav-milter)	24s
check (clambc)	25s
check (clamconf)	21s
check (clamd)	23s
check (clamdscan)	22s
check (clamdtop)	23s
check (clamonacc, (c-thread-pool\|fts\|priv_fts))	20s
check (clamscan)	18s
check (clamsubmit)	19s
check (freshclam)	18s
check (libfreshclam)	18s
check (common)	18s
check (sigtool)	22s
check (examples)	19s
check (win32/compat)	21s
	5m 51s

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