Add regression test: Assertion failure in array bounds inference on array subscript in multi-variable declaration

[john-h-kastner]

For example this function and the corresponding error text:

void h(int *a) {
  int i, j = a[0];
}

3c: /home/cc/checkedc-clang/clang/lib/3C/ArrayBoundsInferenceConsumer.cpp:836: void LengthVarInference::VisitArraySubscriptExpr(clang::ArraySubscriptExpr*): Assertion `CurBB != nullptr && "Array dereference does not belong " "to any basic block"' failed.

This error affects the -alltypes conversion of Lua.

[Machiry]

Fixed. There is a chance of clang CFG not having appropriate basicblock.

[mattmccutchen-cci]

I realize we should probably add a regression test for this. I'll take a stab at it (just copying John's original example) if no one beats me to it.