fix callconv's expression scope

Inve1951 · web-flow · commit 76c9ab4f4f54 · 2021-09-27T23:54:45.000+02:00
should close ziglang#4630
diff --git a/src/AstGen.zig b/src/AstGen.zig
@@ -3081,7 +3081,7 @@ fn fnDecl(
                     .{},
                 );
             }
-            break :blk try expr(
+            break :blk try comptimeExpr(
                 &decl_gz,
                 params_scope,
                 .{ .ty = .calling_convention_type },
