[CIR][CodeGen] Fix std::ofstream fail during CodeGen

[bruteforceboy]

Currently, the following code snippet fails during CodeGen, using clang++ tmp.cpp -fclangir -Xclang -emit-cir -S:

#include <fstream>

void foo(const char *path) {
  std::ofstream fout1(path);
  fout1 << path;
  std::ofstream fout2(path);
  fout2 << path;
}

It fails with:

error: 'cir.yield' op expects parent op to be one of 'cir.if, cir.scope, cir.switch, cir.while, cir.for, cir.await, cir.ternary, cir.global, cir.do, cir.try, cir.array.ctor, cir.array.dtor, cir.call, cir.case'

The relevant part of the CIR dump before verification looks like:

    "cir.br"()[^bb1] : () -> ()
  ^bb1:  // pred: ^bb0
    "cir.yield"() : () -> ()
    "cir.return"() : () -> ()
  }) : () -> ()

Two things are wrong: the YieldOp has cir.func as a parent and there is a cir.return too. These come right after the second destructor for basic_ofstream.

This PR fixes this by checking if there is a terminator and removing (if it exists) before adding an implicit return. I have also added a test that mimics the behavior of std::basic_ofstream.

[bcardosolopes]

Thank you!