[fpc-pascal] Sleep(30) is not reliable?

[AlexeyT]

Details:
Ubuntu 17.4 x64; Lazarus 1.9 trunk, fpc 3.0.2.
I see IDE call stack like this  when i pause app (during loop forever)

SYSTEM_$$_FPSYSCALL$INT64$INT64$$INT64
000000000041E7E0 55                       push   %rbp
000000000041E7E1 4889e5                   mov    %rsp,%rbp
000000000041E7E4 488d6424f0               lea    -0x10(%rsp),%rsp
000000000041E7E9 4889f8                   mov    %rdi,%rax
000000000041E7EC 4889f7                   mov    %rsi,%rdi
000000000041E7EF 0f05                     syscall
000000000041E7F1 483d01f0ffff             cmp $0xfffffffffffff001,%rax
000000000041E7F7 7215                     jb     0x41e80e 
<SYSTEM_$$_FPSYSCALL$INT64$INT64$$INT64+46>
000000000041E7F9 48f7d8                   neg    %rax
000000000041E7FC 4889c7                   mov    %rax,%rdi
000000000041E7FF e87cffffff               callq  0x41e780 
<SYSTEM_$$_SETERRNO$LONGINT>
000000000041E804 48b8ffffffffffffffff     movabs $0xffffffffffffffff,%rax
000000000041E80E c9                       leaveq
000000000041E80F c3                       retq
SYSTEM_$$_FPSYSCALL$INT64$INT64$INT64$$INT64
000000000041E810 55                       push   %rbp
000000000041E811 4889e5                   mov    %rsp,%rbp
000000000041E814 488d6424f0               lea    -0x10(%rsp),%rsp
000000000041E819 4889f8                   mov    %rdi,%rax
000000000041E81C 4889f7                   mov    %rsi,%rdi
000000000041E81F 4889d6                   mov    %rdx,%rsi
000000000041E822 0f05                     syscall
000000000041E824 483d01f0ffff             cmp $0xfffffffffffff001,%rax
<<<<< here IDE stops

Alexey