Makefile: Split man pages into multiple lists

This isn't pretty but makes substitution rules easier and working
correctly.
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

Makefile.am

@@ -420,17 +420,23 @@ src_test_signature_LDADD = \
 # ------------------------------------------------------------------------------
 
 MANPAGES = \
+	$(MANPAGES_3) \
+	$(MANPAGES_8)
+
+MANPAGES_3 = \
 	man/libloc.3 \
-	man/location.8 \
 	man/loc_database_new.3 \
 	man/loc_get_log_priority.3 \
 	man/loc_new.3 \
 	man/loc_set_log_fn.3 \
 	man/loc_set_log_priority.3
 
+MANPAGES_8 = \
+	man/location.8
+
 MANPAGES_TXT   = $(MANPAGES_TXT_3) $(MANPAGES_TXT_8)
-MANPAGES_TXT_3 = $(patsubst %.3,%.txt,$(MANPAGES))
-MANPAGES_TXT_8 = $(patsubst %.8,%.txt,$(MANPAGES))
+MANPAGES_TXT_3 = $(patsubst %.3,%.txt,$(MANPAGES_3))
+MANPAGES_TXT_8 = $(patsubst %.8,%.txt,$(MANPAGES_8))
 MANPAGES_HTML  = $(patsubst %.txt,%.html,$(MANPAGES_TXT))
 MANPAGES_XML   = $(patsubst %.txt,%.xml,$(MANPAGES_TXT))