According to meson.build, tmp.mount is installed under
"prefixdir/'lib/systemd/system'", but for 64bit system, rootlibdir is
/usr/lib64/systemd/system, this make tmp.mount not removed, and /tmp
still mounted as tmpfs filesystem. Fixed by using rootlibexecdir, which
is /usr/lib/systemd/system.
Signed-off-by: Changqing Li <changqing.li@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>