configure.ac: add doxygen documentation building

gstlal-inspiral/configure.ac

@@ -27,6 +27,8 @@ AC_CONFIG_FILES([ \
 	bin/Makefile \
 	share/Makefile \
 	tests/Makefile
+	doc/Doxyfile \
+	doc/Makefile
 ])
 
 
@@ -90,7 +92,8 @@ case `cat /etc/redhat-release 2> /dev/null` in
 esac
 LT_INIT
 PKG_PROG_PKG_CONFIG()
-
+AC_PATH_PROG(DOXYGEN, doxygen)
+AM_CONDITIONAL([COND_DOXYGEN], [test -n "${DOXYGEN}"])
 
 #
 # Check for Python