makefiles: make all, clean and distclean PHONY

Avoid a stat() call for each affected target and also potentially speed
up parallel builds.

From the GNU make manual[1]:

> Phony targets are also useful in conjunction with recursive
> invocations of make (see Recursive Use of make).  In this situation
> the makefile will often contain a variable which lists a number of
> sub-directories to be built.

[...]

> The implicit rule search (see Implicit Rules) is skipped for .PHONY
> targets.  This is why declaring a target as .PHONY is good for
> performance, even if you are not worried about the actual file
> existing.

Commands used to search, replace and cleanup:

    $ find -type f -name '*Makefile.in' -exec sed -i.bak \
      -e 's/^all:/.PHONY: all\nall:/' \
      -e 's/^clean:/.PHONY: clean\nclean:/' \
      -e 's/^distclean:/.PHONY: distclean\ndistclean:/' '{}' +
    $ find -type f -name '*Makefile.in.bak' -exec rm '{}' +

[1]: https://www.gnu.org/software/make/manual/html_node/Phony-Targets.html

1 files changed, 3 insertions, 0 deletions

diff --git a/src/man/Makefile.in b/src/man/Makefile.in
index 1598935ca..3711d5cec 100644
--- a/src/man/Makefile.in
+++ b/src/man/Makefile.in
@@ -1,3 +1,4 @@
+.PHONY: all
 all: firecfg.man firejail.man firejail-login.man firejail-users.man firejail-profile.man firemon.man jailtest.man
 
 include ../common.mk
@@ -5,7 +6,9 @@ include ../common.mk
 %.man: %.txt
         gawk -f ./preproc.awk -- $(MANFLAGS) < $< > $@
 
+.PHONY: clean
 clean:; rm -fr *.man
 
+.PHONY: distclean
 distclean: clean
         rm -fr Makefile