unittests/ASM: Test OF,SF,AF flags for fcomi

unittests/ASM/FEX_bugs/fcomi_flags.asm

@@ -0,0 +1,46 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RBX": "0x0000000000000000"
+  }
+}
+%endif
+
+mov rsp, 0xe8000000
+; RBX accumulates any OF,SF,AF bits (mask 0x890)
+; it must end up 0 if OF,SF,AF are being cleared correctly
+lea rbp, [rel data]
+xor rbx, rbx
+
+%macro run_case 2
+  fld qword [rbp]
+  fld qword [rbp]
+
+  ; %1 = 0x0   -> OF/SF/AF set to 0
+  ; %1 = 0x890 -> OF/SF/AF set to 1
+  pushfq
+  pop rax
+  and rax, ~0x890
+  or rax, %1
+  push rax
+  popfq
+
+  %2
+
+  pushfq
+  pop rcx
+  and rcx, 0x890 ; isolate OF, SF, AF
+  or rbx, rcx
+
+  fstp st0
+  fstp st0
+%endmacro
+
+run_case 0x0,   fcomi st1
+run_case 0x890, fcomi st1
+
+hlt
+
+align 8
+data:
+    dq 1.5