package/jemalloc: add jemalloc-config to _CONFIG_SCRIPTS handling
Fixes (part of) http://autobuild.buildroot.net/results/23fe4365ca65f37eace8265a70fbfb9723b8ee9d/
jemalloc installs a jemalloc-config script, leaking build paths and breaking
reproducible builds (and per-package builds).
Add it to _CONFIG_SCRIPTS so the paths get fixed up for staging and the
script removed from target.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>