[PATCH] Correct syntax of ARM mrc, mrc2 when writing to APSR

[Tim Northover]

Hi Mihail,

> The purpose of the patch is to fix the syntax of ARM mrc and mrc2
> instructions when they are used to write to the APSR. In this case, the
> destination operand should be APSR_nzcv, and the encoding of the target
> should be 0b1111 (same as for PC).

Thanks for looking at this.

The changes look reasonable to me, though I'd probably suggest setting
APSR_NZCV to reserved in ARMBaseRegisterInfo.cpp. Your AltOrders
*should* prevent the register allocator doing anything stupid anyway,
but just in case...

Also, some of disassembly tests would be good. I don't think the
DecodeGPRWithAPSR function is exercised by the assembly tests you
added and none of the existing tests seem to use the 0b1111 encoding.

Cheers.

Tim.