Add missing standard headers. Patch by Joerg Sonnenberger!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122193 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/Program.h"
+#include <cctype>
 using namespace llvm;
 
 /// These are manifest constants used by the bitcode writer. They do not need to