[Linux x86-64] Add preliminary support for syscalls
[Linux x86-64] Use SysRet return type
[Linux x86-64] sysGetCPU syscall added
[Linux X86-64] brk syscall added
[Linux X86-64] getpid syscall
[Linux X86-64] getppid syscall added
[Linux X86-64] getuid/geteuid syscalls added
[Linux X86-64] getgid/getegid syscalls added
[Linux x86-64] gettid syscall added
[Linux x86-64] lseek syscall added