Fix compilation errors with gcc.

Change-Id: If88d4f639658db2d6d71f5abcad563211138fc4a
diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 4c4fbd9..8a7b52e 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -576,6 +576,8 @@
     case Primitive::kPrimFloat:
       return Location::FpuRegisterLocation(XMM0);
   }
+
+  UNREACHABLE();
 }
 
 Location InvokeDexCallingConventionVisitorX86::GetMethodLocation() const {