i#6417: Handle AMD 32-bit syscall instruction.

[ivankyluk]

Handle AMD 32-bit syscall instruction.

The fix is to check for AMD 32-bit SYSCALL in is_at_do_syscall().

Here's more details:

CI x86-32 signalNNNN tests started failing recently. After checking the log, the failures happen on AMD 32-bit system.
Based on the debug logs

AMD:

0xf7f90583 89 cd mov %ecx -> %ebp
0xf7f90585 0f 05 syscall -> %ecx
interp: syscall @ 0xf7f90585
instr_get_opcode(instr): 95
change_prot(0xf7f90000, 0x2000, rwx) => mprotect(0xf7f90000, 0x2000, 7)==2 pages
change_prot(0xf7f90000, 0x2000, r-x) => mprotect(0xf7f90000, 0x2000, 5)==2 pages
set_syscall_method to 3make_writable: pc 0x441fc000 -> 0x441fc000-0x441fe000 0
Just updated syscall routine:
0x441fd240 0f 05 syscall -> %ecx
0x441fd242 a3 5c 29 18 44 mov %eax -> 0x4418295c[4byte]

whereas Intel uses sysenter, and set the syscall_method to SYSCALL_METHOD_SYSENTER:

0xf7f71583 89 e5 mov %esp -> %ebp
0xf7f71585 0f 34 sysenter -> %esp
interp: syscall @ 0xf7f71585
change_prot(0xf7f71000, 0x2000, rwx) => mprotect(0xf7f71000, 0x2000, 7)==2 pages
change_prot(0xf7f71000, 0x2000, r-x) => mprotect(0xf7f71000, 0x2000, 5)==2 pages
set_syscall_method to 2make_writable: pc 0x4845a000 -> 0x4845a000-0x4845c000 0
Just updated syscall routine:
0x4845b240 0f 34 sysenter -> %esp
0x4845b242 a3 5c 09 3e 48 mov %eax -> 0x483e095c[4byte]

Issue: #6417