grcov get more excute times

[yuhui518]

1.cargo new hello_world
2.RUSTFLAGS="-C instrument-coverage" cargo cuild
3.cd target/debug && ./hello_world
4. grcov ./target/debug --binary-path ./target/debug -s . -t html --ignore-not-existing -o ../cov/
then,the result is:

Next, I use the llvm-cov tool to get the same profraw file's code covrage,the result is:

I just only excute the "hello_world" binary one times, the grcov's result is three times, and the llvm-cov's result is correct.

### Tasks

[yuhui518]

The llvm-cov's command is:
1.cd target/debug
2.llvm-profdata merge -sparse *.profraw -o json5format.profdata
3.cd ../..
4.. llvm-cov report
--use-color --ignore-filename-regex='/.cargo/registry'
--instr-profile=target/debug/json5format.profdata
--object target/debug/hello_world
5. llvm-cov show
--use-color --ignore-filename-regex='/.cargo/registry'
--instr-profile=target/debug/json5format.profdata
--object target/debug/hello_world
--show-instantiations --show-line-counts-or-regions