fmt: process C function declarations correctly

vlib/v/ast/str.v

@@ -25,6 +25,9 @@ pub fn (node &FnDecl) str(t &table.Table) string {
 		receiver = '($node.receiver.name $m$name) '
 	}
 	name := node.name.after('.')
+	if node.is_c {
+		name = 'C.$name'
+	}
 	f.write('fn ${receiver}${name}(')
 	for i, arg in node.args {
 		// skip receiver

vlib/v/fmt/fmt.v

@@ -173,9 +173,13 @@ fn (f mut Fmt) stmt(node ast.Stmt) {
 			s := it.str(f.table)
 			// f.write(it.str(f.table))
 			f.write(s.replace(f.cur_mod + '.', '')) // `Expr` instead of `ast.Expr` in mod ast
+			if !it.is_c {
 				f.writeln(' {')
 				f.stmts(it.stmts)
 				f.writeln('}\n')
+			} else {
+				f.writeln('\n')
+			}
 		}
 		ast.ForInStmt {
 			f.write('for ')

vlib/v/fmt/fmt_keep_test.v

@@ -2,6 +2,7 @@ import (
 	os
 	term
 	benchmark
+	v.ast
 	v.fmt
 	v.parser
 	v.table
@@ -44,7 +45,7 @@ fn test_fmt() {
 			continue
 		}
 		table := table.new_table()
-		file_ast := parser.parse_file(ipath, table, .parse_comments, &pref.Preferences{})
+		file_ast := parser.parse_file(ipath, table, .parse_comments, &pref.Preferences{}, &ast.Scope{parent: 0})
 		result_ocontent := fmt.fmt(file_ast, table)
 		if expected_ocontent != result_ocontent {
 			fmt_bench.fail()

vlib/v/fmt/tests/functions_expected.vv

@@ -1,3 +1,5 @@
+fn C.func(arg int) int
+
 fn fn_variadic(arg int, args ...string) {
 	println('Do nothing')
 }

vlib/v/fmt/tests/functions_input.vv

@@ -1,3 +1,5 @@
+fn C.func(arg int) int
+
 fn fn_variadic(arg int, args... string) {
 	println('Do nothing')
 }