cgen: fix codegen for a.index/1, where a is []Fn (#20849)

vlib/builtin/array_index_test.v

@@ -0,0 +1,35 @@
+fn test_index_of_ints() {
+	ia := [1, 2, 3]
+	ii := ia.index(2)
+	dump(ii)
+	assert ii == 1
+}
+
+fn test_index_of_strings() {
+	sa := ['a', 'b', 'c']
+	si := sa.index('b')
+	dump(si)
+	assert si == 1
+}
+
+fn test_index_of_voidptrs() {
+	pa := [voidptr(123), voidptr(45), voidptr(99)]
+	pi := pa.index(voidptr(45))
+	dump(pi)
+	assert pi == 1
+}
+
+//////////
+
+fn a() {}
+
+fn b() {}
+
+fn c() {}
+
+fn test_index_of_fns() {
+	fa := [a, b, c]
+	fi := fa.index(b)
+	dump(fi)
+	assert fi == 1
+}

vlib/v/gen/c/array.v

@@ -1061,7 +1061,7 @@ fn (mut g Gen) gen_array_index_methods() {
 			ptr_typ := g.equality_fn(info.elem_type)
 			fn_builder.writeln('\t\tif (${ptr_typ}_arr_eq(*pelem, v)) {')
 		} else if elem_sym.kind == .function && !info.elem_type.is_ptr() {
-			fn_builder.writeln('\t\tif ( pelem == v) {')
+			fn_builder.writeln('\t\tif ( *pelem == v) {')
 		} else if elem_sym.kind == .map && !info.elem_type.is_ptr() {
 			ptr_typ := g.equality_fn(info.elem_type)
 			fn_builder.writeln('\t\tif (${ptr_typ}_map_eq((*pelem, v))) {')