To run shell tests on Windows Subsystem for Linux, the paths for Windows binaries for JDK tools must use an explicit ".exe" suffix, which is not required in other environments.

This can be achieved by using an environment variable ${EXE_SUFFIX} which can be set to ".exe" or left empty as needed. Upcoming versions of jtreg will set the variable if needed, but even without that, the variable can be set via the jtreg `-e` command-line option.

langtools has only a few shell tests remaining, all in a single directory, and all using a single shared setup script. We should update the setup script to support the use of EXE_SUFFIX.