[Clang][PowerPC] Support constraint 'wi' in asm

From the gcc manual, we can see that the specific limit of wi inline asm is “FP or VSX register to hold 64-bit integers for VSX insns or NO_REGS”. The link is https://gcc.gnu.org/onlinedocs/gcc-8.2.0/gcc/Machine-Constraints.html#Machine-Constraints. We should accept this constraint.

Reviewed By: jsji

Differential Revision: https://reviews.llvm.org/D53265

llvm-svn: 345809

clang/lib/Basic/Targets/PPC.h

@@ -201,6 +201,7 @@ public:
       case 's': // VSX vector register to hold scalar float data
       case 'a': // Any VSX register
       case 'c': // An individual CR bit
+      case 'i': // FP or VSX register to hold 64-bit integers data
         break;
       default:
         return false;