Add KillOldProcesses step before running JSC tests in order to add more stability, and ensure that a build is not impacted by leaked processes from previous build.
Similar to what we do for layout-test and api tests in https://trac.webkit.org/r247242.
Also, we recently added KillOldProcesses between JSC tests re-runs in https://trac.webkit.org/r252700 , we should also add KillOldProcesses before running these tests.
Created attachment 384170 [details]
Sample run: https://ews-build.webkit-uat.org/#/builders/27/builds/11
Committed r252786: <https://trac.webkit.org/changeset/252786>