EmulatorPkg: Add IsSigTermSignaled mechanism.

When Host app receiving SigTerm signal, the background threads may not
receive the same. This IsSigTermSignaled can be used for background
threads to do the graceful termination.

Change-Id: I77374ad2a88b5a015ab8564560cbd95f4bd7ae5d
Hsd-es-id: <HSD-ES bug/ise id>
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
9 files changed