Function return type with bounds-safe interface is not properly checked in checked scope

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#302

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While testing calloc/malloc header file, unexpected errors happen

In checked scope, function having return type, that is unchecked pointer type with bounds-safe interface, is not properly checked in checked scope.
Since it has proper bounds-safe interface, it SHOULD be considered as checked pointer type but compiler generates an error for this

void * calloc(size_t nmemb, size_t size) : byte_count(nmemb * size);
array_ptr<ptr<node_t>> retval : count(size) = calloc(size, sizeof(ptr<node_t>));

[secure-sw-dev-bot]

Comment from @wonsubkim:

While testing checkedc-llvm-test-suite, I have found some missing errors

1. When checking declaration in checked scope, I have missed unexpected type case. Fixed it

2. When generating function call in checked scope, I have generated implicit cast expression for checked pointer type for FunctionToPointerDecay
   In function declaration having KNR parameters, it has empty parameter types
   For function call for KNR function , SemaBounds generates implicit casting expression from incompatible type.
   For call expression, DO NOT generate checked pointer type of function

3. In code generation of call instruction (EmitCallArgs), bounds-safe interface has similar problem to interoperation type
   we SHOULD handle same conversion for Sema.GetCheckedCInteropType
   I have also handled unchecked pointer type with bounds-safe interface not also interop type

[secure-sw-dev-bot]

Comment from @dtarditi:

These issues have been addressed- thanks Wonsub!

For point 2 above, we decided to keep generating an implicit cast to checked pointer type for FunctoinToPointerDecay. We decided to not allow calls to functions declared in the old K&R prototype style in checked scopes. Calls to such functions are treated as no-prototype calls, so there could be mismatches between actual arguments and declared argument.