Overly strict replacement of std. functions

[251]

Standard functions e.g. free are always handled by the Special Function Handler and it is not possible to redefine and execute functions with same name even without Posix runtime and uclibc and incompatible signature:

void free() {
	int a = 42;
	++a;
}

int main(void) {
	free();
}                                                                                                                             

> bin/klee free.bc
KLEE: Using STP solver backend
klee: /klee/lib/Core/SpecialFunctionHandler.cpp:764: void klee::SpecialFunctionHandler::handleFree(klee::ExecutionState&, klee::KInstruction*, std::vector<klee::ref<klee::Expr> >&): Assertion `arguments.size()==1 && "invalid number of arguments to free"' failed.
[...]

We should be more careful here.

Reported by @moyix: https://twitter.com/moyix/status/1450665808976306180