parser: fix sizeof(int) when used as call arg for external function (#5855)

vlib/v/parser/pratt.v

@@ -122,7 +122,10 @@ pub fn (mut p Parser) expr(precedence int) ast.Expr {
 					pos: pos
 				}
 			} else {
+				save_expr_mod := p.expr_mod
+				p.expr_mod = ''
 				sizeof_type := p.parse_type()
+				p.expr_mod = save_expr_mod
 				node = ast.SizeOf{
 					is_type: true
 					typ: sizeof_type

vlib/v/tests/sizeof_test.v

@@ -0,0 +1,6 @@
+import math
+
+fn test_sizeof() {
+	r := math.f32_from_bits(sizeof(int))
+	assert r > 5.6e-45 && r < 5.7e-45
+}