MipsAsmBackend.cpp, PPCAsmBackend.cpp: Fix -Asserts build to appease msvc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145894 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp

@@ -181,6 +181,7 @@ public:
                             const MCAsmLayout &Layout) const {
     // FIXME.
     assert(0 && "RelaxInstruction() unimplemented");
+    return false;
   }
 
   /// RelaxInstruction - Relax the instruction in the given fragment

lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp

@@ -100,6 +100,7 @@ public:
                             const MCAsmLayout &Layout) const {
     // FIXME.
     assert(0 && "RelaxInstruction() unimplemented");
+    return false;
   }