When calling FileSpec::AppendPathComponent() we don't need to include "." in...

When calling FileSpec::AppendPathComponent() we don't need to include "." in the path if m_filename is set to exactly '.'. Previously this would cause a FileSpec object that looked like:

m_directory = "/tmp"
m_filename = "."
                                         
To look like:

m_directory = "/tmp/."
m_filename = "foo.txt"

if "foo.txt" was appended to it. With this fix it will be:

m_directory = "/tmp"
m_filename = "foo.txt"

llvm-svn: 250770