build: make sure autoheader run before autoconf

build: make sure autoheader run before autoconf

autoheader will update ../libtool-2.4.6/libltdl/config-h.in which
autoconf needs, so there comes a race sometimes as below:
 | configure.ac:45: error: required file 'config-h.in' not found
 | touch '../libtool-2.4.6/libltdl/config-h.in'

So make sure autoheader run before autoconf to avoid this race.

* Makefile.am: Have $(lt_configure) depend on $(lt_config_h_in).

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>