Suppress an annoying "unused variable" warning caused by bug 17897.

Clang says that "flow" is unused when building LLD. This patch suppresses it.

Differential Revision: http://llvm-reviews.chandlerc.com/D2573

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199922 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rui314

include/llvm/Support/YAMLTraits.h

@@ -1123,6 +1123,7 @@ operator<<(Output &yout, T &seq) {
         return seq.size();                                                  \
       }                                                                     \
       static _type& element(IO &io, std::vector<_type> &seq, size_t index) {\
+        (void)flow; /* Remove this workaround after PR17897 is fixed */     \
         if ( index >= seq.size() )                                          \
           seq.resize(index+1);                                              \
         return seq[index];                                                  \