Repeated syscall instructions with the same PC found in memtraces

This is to create a new invariant check type for double syscall instructions that have the same PC address and are currently reported as **_Non-explicit control flow has no marker_** invariant error. This will help in identify this specific invariant error in traces.
```
8979242: T141294 ifetch 2 byte(s) @ 0x00007fcf3b9dd9ea 0f 05 syscall -> %rcx %r11
8979243: T141294
8979244: T141294
// 'Non-explicit control flow has no marker' invariant error reported here.
8979245: T141294 ifetch 2 byte(s) @ 0x00007fcf3b9dd9ea 0f 05 syscall -> %rcx %r11
8979246: T141294
```