It does not take a lot for a microprocessor to support the "C" Language efficiently. At a minimum, the micoprocessor must :

(a) Support a "nontrivial stack" and stack-relative memory indexing.
(b) Support 2 index registers to facilitate byte copying
(c) Support multiprecision arithmetic
(d) Support the basic boolean operators, + - * / << >> & | ^

These are not deep concepts to computer designers. Somehow, Intel 8051 managed to blow it on 2 out of 4 of these counts (a) and (b). Atmel's Mega/AVR processor corrects Intel's mistake (b), but it's still true that the 8051 is a bad CPU for running any high-level language that keeps variables on a stack.