We were including sys/syscall.h and asm/unistd.h, since sys/syscall.h
includes asm/unistd.h, sometimes this leads to the redefinition of
defines, breaking the build.

Noticed on ARC with uCLibc.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Link: https://lkml.kernel.org/n/tip-xjpf80o64i2ko74aj2jih0qg@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>