Enable -Wimplicit-fallthrough.

Falling through switch cases on a clang build must now annotate the fallthrough
with the FALLTHROUGH_INTENDED macro.
Bug: 17731372

Change-Id: I836451cd5f96b01d1ababdbf9eef677fe8fa8324
diff --git a/compiler/dex/quick/mips/assemble_mips.cc b/compiler/dex/quick/mips/assemble_mips.cc
index c7e9190..01d1a1e 100644
--- a/compiler/dex/quick/mips/assemble_mips.cc
+++ b/compiler/dex/quick/mips/assemble_mips.cc
@@ -465,6 +465,7 @@
   switch (opcode) {
     case kMipsBal:
       LOG(FATAL) << "long branch and link unsupported";
+      UNREACHABLE();
     case kMipsB:
       unconditional = true;
       break;
@@ -478,6 +479,7 @@
     case kMipsBnez: opcode = kMipsBeqz; break;
     default:
       LOG(FATAL) << "Unexpected branch kind " << opcode;
+      UNREACHABLE();
   }
   LIR* hop_target = NULL;
   if (!unconditional) {