Coverage report: "Unexecuted instantiation:..." for a generic function from multiple crates

[richkadel]

llvm-cov show reports show "Unexecuted instantiation:..." for a generic function used in the declaring crate and an external crate.

The count of total coverage for the generic function is accurate, but the user would not be able to see the individual counts for each type substitution.

This only affects generics used by two different crates (such as a library where the generic function was declared and a binary using that function via extern crate import).

(I'm not sure if a generic declared but not used in a library, but used by two different binaries, with different type substitutions, also has the same problem.)

See src/test/run-make-fulldeps/coverage/lib/used_crate.rs for more details and possible root cause contributors.