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/lib/Makefile.in b/src/lib/Makefile.in
index 681252832..49c8057b3 100644
--- a/src/lib/Makefile.in
+++ b/src/lib/Makefile.in
@@ -1,11 +1,14 @@
 include ../common.mk
 
+.PHONY: all
 all: $(OBJS)
 
 %.o : %.c $(H_FILE_LIST)
         $(CC) $(CFLAGS) $(EXTRA_CFLAGS) $(INCLUDE) -c $< -o $@
 
+.PHONY: clean
 clean:; rm -fr $(OBJS) *.gcov *.gcda *.gcno *.plist
 
+.PHONY: distclean
 distclean: clean
         rm -fr Makefile