DocBook: Make mandocs parallel-safe

Two concurrent calls to cmd_db2man may attempt to compress manual
pages generated by each other.  gzip can then fail due to an input
file having already been compressed and removed.

Move the gzip command to the top-level mandocs target.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Bastian Blank <waldi@debian.org>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
index 5cf621b..0f9c6ff 100644
--- a/Documentation/DocBook/Makefile
+++ b/Documentation/DocBook/Makefile
@@ -54,6 +54,7 @@
 
 MAN := $(patsubst %.xml, %.9, $(BOOKS))
 mandocs: $(MAN)
+	$(if $(wildcard $(obj)/man/*.9),gzip -f $(obj)/man/*.9)
 
 installmandocs: mandocs
 	mkdir -p /usr/local/man/man9/
@@ -159,7 +160,7 @@
             cp $(PNG-$(basename $(notdir $@))) $(patsubst %.html,%,$@); fi
 
 quiet_cmd_db2man = MAN     $@
-      cmd_db2man = if grep -q refentry $<; then xmlto man $(XMLTOFLAGS) -o $(obj)/man $< ; gzip -f $(obj)/man/*.9; fi
+      cmd_db2man = if grep -q refentry $<; then xmlto man $(XMLTOFLAGS) -o $(obj)/man $< ; fi
 %.9 : %.xml
 	@(which xmlto > /dev/null 2>&1) || \
 	 (echo "*** You need to install xmlto ***"; \