Use report_fatal_error instead of unreachable for -fast-isel-abort

Suggestion by Andrea Di Biagio

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 231201
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index d015b0b..d8b79ac 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1182,7 +1182,7 @@
           // Fast isel failed to lower these arguments
           ++NumFastIselFailLowerArguments;
           if (EnableFastISelAbort > 1)
-            llvm_unreachable("FastISel didn't lower all arguments");
+            report_fatal_error("FastISel didn't lower all arguments");
 
           // Use SelectionDAG argument lowering
           LowerArguments(Fn);
@@ -1254,7 +1254,7 @@
           if (EnableFastISelAbort > 2)
             // FastISel selector couldn't handle something and bailed.
             // For the purpose of debugging, just abort.
-            llvm_unreachable("FastISel didn't select the entire block");
+            report_fatal_error("FastISel didn't select the entire block");
 
           if (!Inst->getType()->isVoidTy() && !Inst->use_empty()) {
             unsigned &R = FuncInfo->ValueMap[Inst];
@@ -1297,7 +1297,7 @@
         if (ShouldAbort)
           // FastISel selector couldn't handle something and bailed.
           // For the purpose of debugging, just abort.
-          llvm_unreachable("FastISel didn't select the entire block");
+          report_fatal_error("FastISel didn't select the entire block");
 
         NumFastIselFailures += NumFastIselRemaining;
         break;