$ EmulatorPkg/build.sh run
The build architecture will match your host machine's architecture.
On X64 host machines, you can build + run IA32 mode as well:
$ EmulatorPkg/build.sh -a IA32$ EmulatorPkg/build.sh -a IA32 run
$ EmulatorPkg/build.sh -a IA32
$ EmulatorPkg/build.sh -a IA32 run