[ARM64] Fix 'assert("...")' to be 'assert(0 && "...")'. Otherwise, it is

no assert at all. ;] Some of these should probably be switched to
llvm_unreachable, but I didn't want to perturb the behavior in this
patch.

Found by -Wstring-conversion, which I'll try to turn on in CMake builds
at least as it is finding useful things.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205091 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM64/Disassembler/ARM64Disassembler.cpp

@@ -230,7 +230,7 @@ getVariant(uint64_t LLVMDisassembler_VariantKind) {
   case LLVMDisassembler_VariantKind_ARM64_TLVP:
   case LLVMDisassembler_VariantKind_ARM64_TLVOFF:
   default:
-    assert("bad LLVMDisassembler_VariantKind");
+    assert(0 && "bad LLVMDisassembler_VariantKind");
     return MCSymbolRefExpr::VK_None;
   }
 }