Ignore generated file.
Fix native_compute for systems with a limited size for the command line.

The call to the native compiler can fail due to the sheer amounts of -I
options passed to it. Indeed, it is easy to get the command line to exceed
512KB, thus causing various operating systems to reject it. This commit
avoids the issue by only passing the -I options that matter for the
currently compiled code.

Note that, in the worst case, this commit is still not sufficient on
Windows (32KB max), but this worst case should be rather uncommon and thus
can be ignored for now.

For the record, the command-line size mandated by Posix is 4KB.