tools build feature: Use value assignment form for FEATURE-DUMP file

tools build feature: Use value assignment form for FEATURE-DUMP file

Changing the contents of the FEATURE-DUMP file, so it looks like:

  feature-backtrace=1
  feature-dwarf=0
  feature-fortify-source=1
  feature-sync-compare-and-swap=0

This way it could get included in sub projects, so they won't be forced
to redo features detection.

Also now storing the complete set of features.

Signed-off-by: Jiri Olsa <[email protected]>
Tested-by: Wang Nan <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Zefan Li <[email protected]>
Cc: pi3orama <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>