COFF: Support Windows resource files.

Resource files are data files containing i18n messages, icon images, etc.
MSVC has a tool to convert a resource file to a regular COFF file so that
you can just link that file to embed resources to an executable.

However, you can directly pass resource files to the linker. If you do that,
the linker invokes the tool automatically. This patch implements that feature.

llvm-svn: 239704