It should compile to the same binary, you just don't be able to sign it i guess.
Intel can just give the source, but you can't trust Intel to just give you the same compiler they used, because the compiler might insert a backdoor. You'd need the compiler source, audit it for backdoors, then compile that with a trustworthy compiler. Then use the resulting compiler to compile the ME source.
(Compiler compiler compiler)
It is possible (though somewhat time-intensive) to audit binaries, too. If there is real demand for this, it should be possible to crowdscale the auditing problem over a large group of OSS enthusiasts.
(Reflections on Trusting Trust)
Thanks, I really enjoyed reading it!
Of course that only helps if you trust the toolchain.