Simplify os_file_author interface
In file-author
we call the alien function os_file_author
expecting
to an (alien:* c-call:c-string)
type. But os_file_author
returns
a C string or NULL. I think we can just use c-call:c-string
as the
return type instead.
If so, this gets rid of the compiler note about being unable to optimize away %SAP-ALIEN and forced to do runtime allocation.