[int0x80]

Just a nitpick. Implementation is about the particular compiler and runtime (stdlib) implementation, not the hardware. Hardware is the platform hosting the implementation (this are ISO C-standard defined terms).

A compiler targeting x86 platform can implement sizeof int == 8, or whatever it pleases, as far as C std is concerned.

In practice compilers dont get creative about this. But there are real world cases where stuff is different, for example: http://www.unix.org/version2/whatsnew/lp64_wp.html