mallopt.3: MALLOC_MMAP_THRESHOLD_ and MALLOC_MMAP_MAX_ *do* work in setgid programs

My testing on this point was bogus, overlooking details of
strace(1)'s behavior with setuid programs.

See https://sourceware.org/bugzilla/show_bug.cgi?id=12155

Reported-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
inotify.7: ffix

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>