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
InstrProf: Avoid linear search in a hot loop

Every time we were adding or removing an expression when generating a
coverage mapping we were doing a linear search to try and deduplicate
the list. The indices in the list are important, so we can't just
replace it by a DenseMap entirely, but an auxilliary DenseMap for fast
lookup massively improves the performance issues I was seeing here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218892 91177308-0d34-0410-b5e6-96231b3b80d8