c2a: Fix rust_version calculation

string-typed result groups would cause the comparison to fail with a
type error. Explicitly casting results to integer for comparison, then
back to string for concatenation causes things to work again.

Bug: 234744235
Test: Run tool with no --cargo_bin option (and the following patch)
(thus using local cargo version detection) and observe success.

Change-Id: I91d8de925c1b6eca7c9905ea85e1ad90e01fb1f9
1 file changed