Running jdk's tests to produce coverage report

[Chaliasos, Stefanos]

Hello,

I'm trying to compute code coverage for langtools in the JDK repo on a Ubuntu 18.04 machine using JDK 18 for the compilation. I have run the following commands:

```
cd /home/user
git clone https://github.com/openjdk/jdk.git
cd jdk && bash configure && make jdk && cd ../
git clone https://github.com/openjdk/jtreg.git
cd jtreg
bash make/build.sh --jdk /home/user/jdk/build/linux-x86_64-server-release/jdk/
cd ../jdk
bash configure --with-jtreg=/home/user/jtreg/build/images/jtreg --with-jcov=/home/user/jtreg/build/deps/jcov/
make jcov-image
```

In the last command, I get errors with the following message:

```
Exception details: Unsupported class file major version 62
...
```

and then the message:

```
SEVERE  : wrong command for jlink mods:
....
```

I tried to compile JCOV with JDK 18 but without success. Does anyone know if it is possible to compute code coverage on the master branch?

Kind regards,

Stefanos Chaliasos