`mkstemps` generates a unique temporary file name from a pattern like
`prefixXXXXXXsuffix` where `prefix` and `suffix` can be any string with
only characters that are valid in a filename. The second parameter is
the length of the suffix.
`mkstemp` is `mkstemps` with suffix length 0, so to avoid code
duplication it calls `mkstemps`. It is unlikely this has any
significant performance impact on SerenityOS.
`generate_unique_filename` now takes the suffix length as a `size_t`.
The original behavior of this function is preserved when specifying a
suffix length of 0. All original uses of this function have been
adapted.
`mkstemps()` was added because it is required by version 4.6.3 of the
ccache port.