Get the path to qemu in the following order:
1) From the property platform.plugin.qemu-user.emulator-path
2) If that property is not set, from PATH, building the name of the qemu
binary from the triple in property platform.plugin.qemu-user.architecture
3) If that property is not set, from PATH, building the name of the qemu
binary from the triple in the target
This will allow a user to load a target and run without setting properties,
if qemu is on the PATH and named qemu-<ArchName>
Reviewed By: labath
Differential Revision: https://reviews.llvm.org/D155117
be88462cd6