Add flag for the SoftFail case of the LLVM disassembler.

[Rot127]

Your checklist for this pull request

• I've documented or updated the documentation of every API function and struct this PR changes.
• I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

The LLVM disassembler returns SoftFail if the instruction can be decoded, but it is illegal due to other reasons.

E.g. because it uses operands it is not allowed to use or the instructions is invalid in a given context.

New cstool output:

cstool arm "0xf0, 0x00, 0xf0, 0xe7, 0x07, 0xB0, 0xBD, 0xE8, 0xf0, 0x00, 0xf0, 0xe7"
 0  f0 00 f0 e7  udf	#0
 4  07 b0 bd e8  pop	{r0, r1, r2, r12, sp, pc}	; Illegal instruction
 8  f0 00 f0 e7  udf	#0

Test plan

Added.

I didn't went through the trouble looking up a SoftFail case for each architecture.
But added the instructions from the issues and null-hypothesis test cases.

Can't reproduce the instruction sequence from #1991. No idea what I did there. But it is not added as use case.

Closing issues

closes #2703
closes #1991

[Rot127]

cc @Rosayxy

[Rosayxy]

I checked the instruction, it works as expected. Seems great!