mountinfo: make the path to /proc/mounts a constant
mountinfo: make the path to /proc/mounts a constant

This path should not be hard coded in the open call.
Linux prior to 2.4.19 did not have /proc/self/mounts, so for now I'm
making this value /proc/mounts everywhere, but that may change to
/proc/self/mounts on linux; I'm not sure we should care about <2.4.19.

X-Gentoo-Bug: 604646
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=604646

williamh/openrc,williamh/openrc,OpenRC/openrc,dwfreed/openrc,OpenRC/openrc,dwfreed/openrc,OpenRC/openrc,dwfreed/openrc,williamh/openrc