mmap-basic fails on arm64.

 4: read samples using the mmap interface: read samples using the mmap interface: FAILED!

This is because arm64 doesn't come with getpgrp() syscall. The syscall
is a BSD compatibility wrapper, Archs that don't define
__ARCH_WANT_SYS_GETPGRP do not have this. Remove it, since getpgid is
already used in the testcase.
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1429192375-13706-4-git-send-email-riku.voipio@linaro.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>