COFF: Support /manifest{,uac,dependency,file} options.

The linker has to create an XML file for each executable.
This patch supports that feature.

You can optionally embed an XML file to an executable as .rsrc
section. If you choose to do that (by passing /manifest:embed
option), the linker has to create a textual resource file
containing an XML file, compile that using rc.exe to a binary
resource file, conver that resource file to a COFF file using
cvtres.exe, and then link that COFF file. This patch implements
that feature too.

llvm-svn: 239978