[DWARF] Strange line information at O1

Compiling the following example with `-g -O1` with emcc 2.0.12 produces a bunch of strange entries in the DWARF line table:

```
#include
int a = 0;

void Func(int a) {
{
int a = 2;
{
int a = 3;
printf("%p %d\n", &a, a);
}
printf("%p %d\n", &a, a);
}
printf("%p %d\n", &a, a);
}

int main() {
Func(1);
printf("%p %d\n", &a, a);
}
```

I get a line table looking like this:
```
0x0000000000000006 4 0 1 0 0 is_stmt
0x000000000000001a 6 9 1 0 0 is_stmt prologue_end
0x0000000000000021 9 7 1 0 0 is_stmt
0x0000000000000028 8 11 1 0 0 is_stmt
0x000000000000002f 9 7 1 0 0 is_stmt
0x0000000000000044 11 5 1 0 0 is_stmt
0x0000000000000046 11 27 1 0 0
0x000000000000004b 11 5 1 0 0
0x0000000000000058 9 7 1 0 0 is_stmt
0x000000000000005b 11 5 1 0 0 is_stmt
0x0000000000000063 13 3 1 0 0 is_stmt
0x0000000000000065 13 25 1 0 0
0x000000000000006a 13 3 1 0 0
0x0000000000000077 9 7 1 0 0 is_stmt
0x000000000000007a 13 3 1 0 0 is_stmt
0x000000000000007f 14 1 1 0 0 is_stmt
0x0000000000000088 14 1 1 0 0 is_stmt end_sequence
```

As you can see, the execution seems to jump back to line 9 before every printf. AFAICT the code offsets for those jumping lines are instructions pushing the first argument to printf (the string). That argument is just an `i32.const 1024`, which means the line table entries are bogus.