This patch adds a new flag "-coff-imports" to llvm-readobj.

This patch adds a new flag "-coff-imports" to llvm-readobj.
When the flag is given, the command prints out the COFF import table.

Currently only the import table directory will be printed.
I'm going to make another patch to print out the imported symbols.

The implementation of import directory entry iterator in
COFFObjectFile.cpp was buggy. This patch fixes that too.

http://reviews.llvm.org/D5569

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218891 91177308-0d34-0410-b5e6-96231b3b80d8