prune the #includes in raw_ostream.h by moving a 
member out of line. ftostr is not particularly speedy,
so that method is presumably not perf sensitive.

llvm-svn: 79885
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 99d2988..7a67fac 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include <vector>
 using namespace llvm;
 
 class MachObjectWriter;