C++17 compatibility: make WITH_TIDY=1 happy again.

Bug: http://b/111067277
Test: builds
Change-Id: I8b69ea3815e14bb6eb27f40c0dd01a85b340a355
diff --git a/compiler/optimizing/induction_var_analysis.cc b/compiler/optimizing/induction_var_analysis.cc
index a4d638f..3a10d58 100644
--- a/compiler/optimizing/induction_var_analysis.cc
+++ b/compiler/optimizing/induction_var_analysis.cc
@@ -1074,8 +1074,8 @@
           && lower_value >= upper_value;
     default:
       LOG(FATAL) << "CONDITION UNREACHABLE";
+      UNREACHABLE();
   }
-  return false;  // not certain, may be untaken
 }
 
 bool HInductionVarAnalysis::IsFinite(InductionInfo* upper_expr,
@@ -1099,8 +1099,8 @@
       return (IsAtLeast(upper_expr, &value) && value >= (min - stride_value));
     default:
       LOG(FATAL) << "CONDITION UNREACHABLE";
+      UNREACHABLE();
   }
-  return false;  // not certain, may be infinite
 }
 
 bool HInductionVarAnalysis::FitsNarrowerControl(InductionInfo* lower_expr,