Fix clang -Wimplicit-fallthrough warnings across llvm, NFC

This patch should not introduce any behavior changes. It consists of
mostly one of two changes:
1. Replacing fall through comments with the LLVM_FALLTHROUGH macro
2. Inserting 'break' before falling through into a case block consisting
   of only 'break'.

We were already using this warning with GCC, but its warning behaves
slightly differently. In this patch, the following differences are
relevant:
1. GCC recognizes comments that say "fall through" as annotations, clang
   doesn't
2. GCC doesn't warn on "case N: foo(); default: break;", clang does
3. GCC doesn't warn when the case contains a switch, but falls through
   the outer case.

I will enable the warning separately in a follow-up patch so that it can
be cleanly reverted if necessary.

Reviewers: alexfh, rsmith, lattner, rtrieu, EricWF, bollu

Differential Revision: https://reviews.llvm.org/D53950

llvm-svn: 345882
diff --git a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
index 2e70d35..79e0c00 100644
--- a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -767,13 +767,13 @@
 
   ~MipsOperand() override {
     switch (Kind) {
-    case k_Immediate:
-      break;
     case k_Memory:
       delete Mem.Base;
       break;
     case k_RegList:
       delete RegList.List;
+      break;
+    case k_Immediate:
     case k_RegisterIndex:
     case k_Token:
       break;