cgen: fix variadic on translated (fix #25862) (#25876)

Author: felipensp

vlib/v/ast/ast.v

@@ -832,6 +832,7 @@ pub mut:
 	is_file_translated     bool // true, when the file it resides in is `@[translated]`
 	is_static_method       bool // it is a static method call
 	is_variadic            bool
+	is_c_variadic          bool // it is a C variadic
 	args                   []CallArg
 	expected_arg_types     []Type
 	comptime_ret_val       bool

vlib/v/checker/fn.v

@@ -2957,6 +2957,7 @@ fn (mut c Checker) check_expected_arg_count(mut node ast.CallExpr, f &ast.Fn) !
 	}
 	if f.is_variadic {
 		node.is_variadic = f.is_variadic
+		node.is_c_variadic = f.is_c_variadic
 		min_required_params--
 		c.markused_array_method(!c.is_builtin_mod, '')
 	} else {

vlib/v/gen/c/fn.v

@@ -2632,7 +2632,7 @@ fn (mut g Gen) call_args(node ast.CallExpr) {
 			}
 		} else {
 			if variadic_count > 0 {
-				if g.pref.translated || g.file.is_translated {
+				if node.is_c_variadic {
 					// Handle passing e.g. C string literals to `...` C varargs:
 					// void DEH_snprintf(char *buffer, size_t len, const char *fmt, ...)
 					// deh_snprintf(buffer, 9, c'STCFN%.3d', j++)

vlib/v/parser/fn.v

@@ -485,6 +485,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	params_t, are_params_type_only, mut is_variadic, mut is_c_variadic := p.fn_params()
 	if is_c2v_variadic {
 		is_variadic = true
+		is_c_variadic = true
 	}
 	params << params_t
 	// Return type

vlib/v/tests/fns/translated_variadic_test.v

@@ -0,0 +1,10 @@
+@[translated]
+module main
+
+fn foo(args ...string) {
+	println(args)
+}
+
+fn test_main() {
+	foo(42.str(), 'bar')
+}