linux.core: optimize system calls for memory usage

linux.core: optimize system calls for memory usage

Drop the arguments and return value and internalize the
Strings.

Change-Id: Id8ab76df2679917e1bcd3e76457ee8f6632bb5b0
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/72939
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>