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

Bug: http://b/111067277
Test: builds
Change-Id: I8b69ea3815e14bb6eb27f40c0dd01a85b340a355
diff --git a/compiler/jni/quick/x86/calling_convention_x86.cc b/compiler/jni/quick/x86/calling_convention_x86.cc
index ad58e38..71e6019 100644
--- a/compiler/jni/quick/x86/calling_convention_x86.cc
+++ b/compiler/jni/quick/x86/calling_convention_x86.cc
@@ -257,7 +257,7 @@
 
 ManagedRegister X86JniCallingConvention::CurrentParamRegister() {
   LOG(FATAL) << "Should not reach here";
-  return ManagedRegister::NoRegister();
+  UNREACHABLE();
 }
 
 FrameOffset X86JniCallingConvention::CurrentParamStackOffset() {