arch: Drop sysctl support if built against glibc

arch: Drop sysctl support if built against glibc

Since glibc 2.30 the sysctl() function has been declared deprecated and
it will be deleted in future versions. This patch removes the support
for the sysctl system call in SE mode (which is currently serviced
calling the sysctl() function) if gem5 is built against glibc, keeping
it with other libc implementations, as a temporary measure to prevent
the generation of a compilation error. Note that this system call in
gem5 is only supported for the arm/freebsd architecture.

Change-Id: Ie5fcb983d15c0a27c7820d24250d7ae5dbe12355
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21519
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>