sys/test: add more tests for bitfields

Add tests for issue #1542

The correct results are obtained with the following program:

struct foo {
	unsigned char	f0;
	unsigned int	f1:4;
	unsigned short	f2:4;
};

struct bar {
	char f0;
	struct foo foo;
};

int main() {
	struct bar y;
	memset(&y, 0, sizeof(y));
	y.f0 = 0x12;
	y.foo.f0 = 0x34;
	y.foo.f1 = 0x56;
	y.foo.f2 = 0x78;
	int i;
	for (i = 0; i < sizeof(y); i++)
		printf("%02x", ((unsigned char*)&y)[i]);
	printf("\n");
}

sys/test/exec.txt

@@ -15,6 +15,12 @@ compare_data [
 	bf1	syz_bf_struct1
 	bf2	syz_bf_struct2
 	bf3	syz_bf_struct3
+	bf4	syz_bf_align[syz_bf_struct4]
+	bf5	syz_bf_align[syz_bf_struct5]
+	bf6	syz_bf_align[syz_bf_struct6]
+	bf7	syz_bf_align[syz_bf_struct7]
+	bf8	syz_bf_align[syz_bf_struct8]
+	bf9	syz_bf_align[syz_bf_struct9]
 	str	string
 	blob	array[int8]
 	arr16be	array[int16be]
@@ -27,3 +33,42 @@ align0 {
 	f3	int16
 	f4	int64
 }
+
+syz_bf_struct4 {
+	f0	int8
+	f1	int32:4
+	f2	int8
+}
+
+syz_bf_struct5 {
+	f0	int8
+	f1	int32:4
+}
+
+syz_bf_struct6 {
+	f0	int8
+	f1	int16:4
+	f2	int8
+}
+
+syz_bf_struct7 {
+	f0	int8
+	f1	int16:4
+}
+
+syz_bf_struct8 {
+	f0	int8
+	f1	int32:4
+	f2	int16:4
+}
+
+syz_bf_struct9 {
+	f0	int8
+	f1	int16:4
+	f2	int16:4
+}
+
+type syz_bf_align[T] {
+	f0	int8
+	f1	T
+}