Use report_fatal_error, not llvm_unreachable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104899 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp b/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
index fc73938..a5a2869 100644
--- a/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
+++ b/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
@@ -1066,7 +1066,7 @@
     case 'Q':
     case 'R':
     case 'H':
-      llvm_unreachable("llvm does not support 'Q', 'R', and 'H' modifiers!");
+      report_fatal_error("llvm does not support 'Q', 'R', and 'H' modifiers!");
       return true;
     }
   }