Make linux_syscall_support.h compilable with -Wstrict-prototypes

Ensure that some functions are defined as taking no arguments rather
than (in C) taking unspecified arguments.  This prevents GCC from
giving errors when compiling with "-Wstrict-prototypes -Werror".

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3114
TEST=run "gcc -Wstrict-prototypes lss/linux_syscall_support.h"

Review URL: https://codereview.chromium.org/11301032

git-svn-id: http://linux-syscall-support.googlecode.com/svn/trunk@17 829466d3-f3f5-3ae4-62ad-de35cf9bba21