Build System: Fix build failure caused by recent CLI improvements.

We use the editline library to help with filename completion in our CLI
interface.  Some systems failed to find the header when included from
loader.c.  This is fixed by setting the proper CFLAGS for the build of
loader.o.

ASTERISK-27378

Change-Id: Ib7fd496f1d7ed48141a2eadd5dd61cab2f2308be