install pkg-config configuration files

Suggested by Jeroen Meijer.

* spot/libspot.pc.in, spot/ltsmin/libspotltsmin.pc.in: New file.
* spot/Makefile.am, spot/ltsmin/Makefile.am: Distribute them, and
install their derived version.
* spot/.gitignore: Ignore *.pc files.
* debian/libbddx-dev.install, debian/libspot-dev.install: Ship
those *.pc files.
* NEWS: Mention it.

spot/ltsmin/Makefile.am

@@ -1,6 +1,6 @@
 ## -*- coding: utf-8 -*-
-## Copyright (C) 2011, 2013, 2014, 2015, 2016 Laboratoire de Recherche
-## et Developpement de l'Epita (LRDE).
+## Copyright (C) 2011, 2013, 2014, 2015, 2016, 2017 Laboratoire de
+## Recherche et Developpement de l'Epita (LRDE).
 ##
 ## This file is part of Spot, a model checking library.
 ##
@@ -34,3 +34,18 @@ libspotltsmin_la_LIBADD = \
   $(LIBLTDL) -lpthread
 libspotltsmin_la_LDFLAGS = -no-undefined $(SYMBOLIC_LDFLAGS)
 libspotltsmin_la_SOURCES = ltsmin.cc
+
+
+EXTRA_DIST = $(srcdir)/libspotltsmin.pc.in
+pkgconfigdir = $(libdir)/pkgconfig
+nodist_pkgconfig_DATA = libspotltsmin.pc
+
+libspotltsmin.pc: $(srcdir)/libspotltsmin.pc.in
+	sed -e 's![@]prefix[@]!$(prefix)!g' \
+	    -e 's![@]exec_prefix[@]!$(exec_prefix)!g' \
+	    -e 's![@]includedir[@]!$(includedir)!g' \
+	    -e 's![@]libdir[@]!$(libdir)!g' \
+	    -e 's![@]PACKAGE_VERSION[@]!$(PACKAGE_VERSION)!g' \
+	$(srcdir)/libspotltsmin.pc.in > $@
+
+DISTCLEANFILES = libspotltsmin.pc

spot/ltsmin/libspotltsmin.pc.in

@@ -0,0 +1,12 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+includedir=@includedir@
+libdir=@libdir@
+
+Name: Spot-LTSmin
+Description: Access to LTSmin-compatible state-space in Spot
+URL: https://spot.lrde.epita.fr/
+Version: @PACKAGE_VERSION@
+Cflags: -I${includedir}
+Libs: -L${libdir} -lspotltsmin
+Requires: libspot