Only request permitted capabilities in non-libcap builds

Only request permitted capabilities in non-libcap builds

While libcap-enabled builds check whether any capability named requests
is within the permitted capability set, non-libcap builds just try
requesting them, which potentially causes a misleading error message to
be output ("Operation not permitted: please ensure that the capset
kernel module is loaded").  Ensure non-libcap builds also check whether
any requested capability is within the permitted capability set.

(cherry picked from commit 8c66f32e53761dfa033dab3d366594683d24ce28)