"The real problem here is (and I have seeen it) that a timed loop in "C" may change when a newer version of the compiler is used"

Absolutely!
But you might not even have to wait for a new compiler revision; if you just change a bit of code nearby it could enable the compiler to introduce (or force it to stop using) some different optimisation technique(s) - and "suddenly" your loop timing is all to pot!

To be absolutely certain, you would have to repeat the examination of the generated code every single time you re-compiled.
It'd be easier to do it in Assembler in the first place (or at least get the Compiler to generate Assembler, and then use that).