tools build: Correct bpf fixdep dependencies

The dependencies in tools/lib/bpf/Makefile are incorrect. Before we
recurse to build $(BPF_IN_STATIC), we need to build its 'fixdep'
executable.

I can't use the usual shortcut from Makefile.include:

  <target>: <sources> fixdep

because its 'fixdep' target relies on $(OUTPUT), and $(OUTPUT) differs
in the parent 'make' versus the child 'make' -- so I imitate it via
open-coding.

I tweak a few $(MAKE) invocations while I'm at it, because
1. I'm adding a new recursive make; and
2. these recursive 'make's print spurious lines about files that are "up
   to date" (which isn't normally a feature in Kbuild subtargets) or
   "jobserver not available" (see [1])

I also need to tweak the assignment of the OUTPUT variable, so that
relative path builds work. For example, for 'make tools/lib/bpf', OUTPUT
is unset, and is usually treated as "cwd" -- but recursive make will
change cwd and so OUTPUT has a new meaning. For consistency, I ensure
OUTPUT is always an absolute path.

And $(Q) gets a backup definition in tools/build/Makefile.include,
because Makefile.include is sometimes included without
tools/build/Makefile, so the "quiet command" stuff doesn't actually work
consistently without it.

After this change, top-level builds result in an empty grep result from:

  $ grep 'cannot find fixdep' $(find tools/ -name '*.cmd')

[1] https://www.gnu.org/software/make/manual/html_node/MAKE-Variable.html
If we're not using $(MAKE) directly, then we need to use more '+'.

Signed-off-by: Brian Norris <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Richter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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