(noinst_LTLIBRARIES): ... this.
* src/ltlenv/Makefile.am, src/ltlast/Makefile.am,
src/ltlparse/Makefile.am: Likewise.
* src/Makefile.am (lib_LTLIBRARIES, libspot_la_SOURCES,
libspot_la_LIBADD): New variable.   Build a libspot.la library
from all the sub-libraries.