cgo: rename reserved field names like type

This commit renames reserved field names like `type` to `_type`, and in
turn renames those fields as well (recursively). This avoids name
clashes when a C struct contains a field named `type`, which is a
reserved keyword in Go.

For some details, see:
https://golang.org/cmd/cgo/#hdr-Go_references_to_C

cgo/libclang.go

@@ -605,6 +605,7 @@ func (p *cgoPackage) makeASTRecordType(cursor C.GoCXCursor, pos token.Pos) (*ast
 	}{fieldList, p, &inBitfield, &bitfieldNum, &bitfieldList})
 	defer storedRefs.Remove(ref)
 	C.tinygo_clang_visitChildren(cursor, C.CXCursorVisitor(C.tinygo_clang_struct_visitor), C.CXClientData(ref))
+	renameFieldKeywords(fieldList)
 	switch C.tinygo_clang_getCursorKind(cursor) {
 	case C.CXCursor_StructDecl:
 		return &ast.StructType{