llvm-readobj: add support to dump COFF export tables

This enhances llvm-readobj to print out the COFF export table, similar to the
-coff-import option.  This is useful for testing in lld.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225120 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-readobj/ObjDumper.h

@@ -45,6 +45,7 @@ public:
 
   // Only implemented for PE/COFF.
   virtual void printCOFFImports() { }
+  virtual void printCOFFExports() { }
   virtual void printCOFFDirectives() { }
   virtual void printCOFFBaseReloc() { }