[CIR][Codegen] Fixes function ptrs in recursive types (llvm#328)

Since recursive types were perfectly fixed, we can safely remove the
assert that prevented functons types generation for the case of
incomplete types. The test is added - just to show that everything is ok
for such kind of functions.

Author: gitoleg

clang/lib/CIR/CodeGen/CIRGenTypes.cpp

@@ -260,11 +260,6 @@ mlir::Type CIRGenTypes::ConvertFunctionTypeInternal(QualType QFT) {
   // the function type.
   assert(isFuncTypeConvertible(FT) && "NYI");
 
-  // While we're converting the parameter types for a function, we don't want to
-  // recursively convert any pointed-to structs. Converting directly-used
-  // structs is ok though.
-  assert(RecordsBeingLaidOut.insert(Ty).second && "NYI");
-
   // The function type can be built; call the appropriate routines to build it
   const CIRGenFunctionInfo *FI;
   if (const auto *FPT = dyn_cast<FunctionProtoType>(FT)) {

clang/test/CIR/CodeGen/fun-ptr.c

@@ -11,6 +11,16 @@ typedef struct {
 
 typedef int (*fun_t)(Data* d);
 
+struct A;
+typedef int (*fun_typ)(struct A*);
+
+typedef struct A {
+  fun_typ fun;  
+} A;
+
+// CIR: !ty_22A22 = !cir.struct<struct "A" {!cir.ptr<!cir.func<!cir.int<s, 32> (!cir.ptr<!cir.struct<struct "A">>)>>} #cir.record.decl.ast>
+A a = {(fun_typ)0};
+
 int extract_a(Data* d) {
     return d->a;
 }