Don't call clock_getres in sysconf.

There are a hundred other reasons why we can't run on kernels old enough
to not have all the clocks covered by sysconf.

This was causing trouble for jemalloc 4.1.0 in a seccomp-constrained process
because jemalloc 4.1.0 introduced a call to sysconf that caused us to make
clock_getres syscalls for the first time, leading to SIGSYS.

Bug: http://b/27408522

(cherry picked from commit d2b8de2c)

Change-Id: Id46a0f2c2804c597a8c9091690a8a1fc4a65f4cd