makefiles: stop failing when config.mk does not exist

This allows running `make clean` and `make distclean` (and possibly
others) without having to run ./configure beforehand.

Note that some packaging-related targets still depend on the existence
of generated files.  For example:

* dist: config.mk
* deb: config.sh

Commands used to search and replace:

    $ git grep -Elz 'include *([^ ]*/)?config.mk' | xargs -0 -I '{}' \
      sh -c "printf '%s\n' \
      \"\$(sed -E 's|^include *(([^ ]*/)?config.mk)|-include \1|' '{}')\" >'{}'"

Relates to #5140.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/man/Makefile b/src/man/Makefile
index c83a4b7eb..b786e1ca9 100644
--- a/src/man/Makefile
+++ b/src/man/Makefile
@@ -2,7 +2,7 @@
 all: firecfg.man firejail.man firejail-login.man firejail-users.man firejail-profile.man firemon.man jailcheck.man
 
 ROOT = ../..
-include $(ROOT)/config.mk
+-include $(ROOT)/config.mk
 
 %.man: %.txt
         gawk -f ./preproc.awk -- $(MANFLAGS) < $< > $@