[COFF] Dump string table size for COFF file headers

I couldn't find this info in any other dumper, so it might as well be
here.
diff --git a/llvm/tools/llvm-readobj/COFFDumper.cpp b/llvm/tools/llvm-readobj/COFFDumper.cpp
index 08031ae..af19a16 100644
--- a/llvm/tools/llvm-readobj/COFFDumper.cpp
+++ b/llvm/tools/llvm-readobj/COFFDumper.cpp
@@ -629,6 +629,7 @@
     W.printHex   ("TimeDateStamp", FormattedTime, Obj->getTimeDateStamp());
     W.printHex   ("PointerToSymbolTable", Obj->getPointerToSymbolTable());
     W.printNumber("SymbolCount", Obj->getNumberOfSymbols());
+    W.printNumber("StringTableSize", Obj->getStringTableSize());
     W.printNumber("OptionalHeaderSize", Obj->getSizeOfOptionalHeader());
     W.printFlags ("Characteristics", Obj->getCharacteristics(),
                     makeArrayRef(ImageFileCharacteristics));