Fix some unused warnings

make: indent preprocessor directives consistently

As seen in share/misc/style.

make(1): remove do-not-format markers from comments

These markers had been used inconsistently. Furthermore the source code
had not been formatted automatically before 2020 at all, otherwise there

make(1): remove do-not-format markers from comments

These markers had been used inconsistently. Furthermore the source code
had not been formatted automatically before 2020 at all, otherwise there
wouldn't have been any trailing whitespace left.

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make(1): use space instead of tab for preprocessor directives

make(1): use comparisons in boolean expressions

The generated code stays exactly the same.

make(1): remove redundant parentheses from sizeof operator

The parentheses are only needed if the argument is a type, not an
expression.

Use O_CLOEXEC and save a syscall.

Reviewed by: riastradh

filemon_dev:filemon_open need FD_CLOEXEC

We need to mark the fd for filemon FD_CLOEXEC
so that when we call filemon_close() the device is
closed and unflushed data written to our temp file.

Per sjg's suggestion, split filemon API into separate back ends.

By default we use the ktrace back end, but the /dev/filemon back end
is available as a compile-time option, by setting USE_FILEMON=de

Per sjg's suggestion, split filemon API into separate back ends.

By default we use the ktrace back end, but the /dev/filemon back end
is available as a compile-time option, by setting USE_FILEMON=dev in
make. sjg raised concerns about ktrace performance and would like to
continue using /dev/filemon on FreeBSD (which has seen more
maintenance kernel-side) without forking make.

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