C++: Do not generate this parameters and read/write side effects from static member functions

[MathiasVP]

Previously, when generating IR for code such as

struct A {
  static void f();
};
...
a.f();

(i.e., a qualified call to a static member function as if it was non-static)
we would generate a this parameter and read/write side effect instructions for parameter -1.

This PR removes the 'this' parameter and read/write side effects for such calls. The case for calls of the form A::f() remains unchanged as this was already generated correctly.

This is the simplest fix I could find that still generate the qualifier without using it. That means that we still generate the call to foo() in an example as:

struct A {
  static void f();
};
A* getAnA();
...
getAnA()->f();

even though the result of getAnA() isn't used as a this parameter.

An implication of this implementation is that TranslatedFunctionCall::getQualifier() can exist even though TranslatedFunctionCall::hasQualifier() doesn't match and TranslatedFunctionCall::getQualifierResult doesn't exist.

[jbj]

LGTM, but I would welcome a second opinion from @rdmarsh2 or @dbartol.

[dbartol]

Doesn't this hold for all non-member functions as well?

[MathiasVP]

Good point! I've fixed this in 6c7e1cd. There are no changes in the tests as TranslatedFunctionCall::getQualifierResult() would fail for non-member functions anyway.