Template functions share the same lines in source files, so the common
container of lines' properties cannot be used to calculate the coverage
statistics of individual functions.
> cat tmpl.cpp
template <int N> int test() { return N; }
int main() { return test<1>() + test<2>(); }
> clang++ --coverage tmpl.cpp -o tmpl
> ./tmpl
> llvm-cov gcov tmpl.cpp -f
...
Function '_Z4testILi1EEiv'
Lines executed:100.00% of 1
Function '_Z4testILi2EEiv'
Lines executed:-nan% of 0
...
> llvm-cov-patched gcov tmpl.cpp -f
...
Function '_Z4testILi1EEiv'
Lines executed:100.00% of 1
Function '_Z4testILi2EEiv'
Lines executed:100.00% of 1
...
Differential Revision: https://reviews.llvm.org/D121390
