x87: fist and frndint doesn't respect rounding mode

Subject: https://github.com/rfalke/decompiler-subjects/blob/master/from_holdec/i386_x87_fpu/ia32_elf/subject.exe
Output:
```
int32_t FIST(void) {
// 0x804a6e0
puts("FIST:\n RC=00: to nearest\n RC=01: down to -inf\n RC=10: up to +inf\n RC=11: to zero\n");
printf(" FISTT(%f): should=12 is=%d\n", 12.7, 12);
printf(" FIST(%f,RC=00): should=13 is=%d\n", 12.7, 12);
printf(" FIST(%f,RC=01): should=12 is=%d\n", 12.7, 12);
printf(" FIST(%f,RC=10): should=13 is=%d\n", 12.7, 12);
printf(" FIST(%f,RC=11): should=12 is=%d\n", 12.7, 12);
printf(" FISTT(%f): should=-7 is=%d\n", -7.1, -7);
printf(" FIST(%f,RC=00): should=-7 is=%d\n", -7.1, -7);
printf(" FIST(%f,RC=01): should=-8 is=%d\n", -7.1, -7);
printf(" FIST(%f,RC=10): should=-7 is=%d\n", -7.1, -7);
printf(" FIST(%f,RC=11): should=-7 is=%d\n", -7.1, -7);
return 0;
}
```

Some of these 12 and -7 should be other numbers.

Start by reproducing the behavior with the subject executable linked in the issue and inspect the generated FIST output for each x87 rounding-control mode. Compare FIST and frndint results with the expected values shown in the report; done means the affected rounding modes produce the documented integer results for positive and negative inputs.

Written by the indexing model from the issue text.