<systemlib/err.h> --> "systemlib/err.h" that fix_headers.sh
would miss because it comes after code it doesn't understand.
Effectively remove the '__EXPORT extern perf_counter_t perf_alloc('
line, because currently perf_alloc is defined to be NULL, and
after running fix_headers.sh that happens *before* this header
is included (the order of headers will be changed).
Do not define NULL to be (void*)0: that only works for C.
In fact, the conversions needed for NULL are so full of exceptions
that standard C++ introduced a new *keyword*: nullptr.
That's what we really should be using for C++ code.
In this case I just include the correct header to define NULL
the correct way.
Not really related to the header line:
Removed an #include <time.h> because I noted that px4_time.h
was already included... and moved a #include <sys/time.h>
to the top of the file (not really a fan of including headers
in the middle unless absolutely necessary).
Removed a include of queue.h because I noted it wasn't used.
Beat Küng