Allow the user to select the arquitecture to compile about eclipser

[jchoi2022]

This seems to be a good idea. I will fix Makefile so one can build Eclipser for specific architecture, with make x86 and make x64.

[jchoi2022]

I updated build scripts and Makefile in ce47d08. Now one can run make x86 or make x64 to specify target architecture, which reduces QEMU build time. Running make will build QEMU for both architectures.

Note that even if you run make x64, running make in the next time will try to build QEMU for x86 architecture. Therefore, you should stick to make x64 in the subsequent builds, too. Actually this hassle can be avoided with a little fix, but it will make our Makefile somewhat hacky.

[ggrieco-tob]

Thanks!