BUILD: makefile: add an EXTRAVERSION variable to ease local naming

Sometimes it's desirable to append local version naming to packages,
and currently it can only be done using SUBVERS which is already set
by default to the git commit ID and patch count since last known tag,
making the addition a bit complicated.

Let's just add a new EXTRAVERSION field that is empty by default, and
systematically appended verbatim to the version string everywhere. This
way it becomes trivial to append some local strings, such as:

   make TARGET=foo EXTRAVERSION=+$(quilt applied|wc -l)
   -> 2.3-dev5-5018aa-15+1

or :

   make TARGET=foo EXTRAVERSION=-$(date +%F)
   -> 2.3-dev5-5018aa-15-20200110

Let's be careful not to add double quotes (used as the string delimiter)
nor spaces (which can confuse version parsers on the output). The extra
version is also used to name a tarball. It's always pre-initialized to an
empty string so that it's not accidently inherited from the environment.
It's not reported in "make version" to avoid fooling tools (it would be
pointless anyway).

As a side effect it also becomes possible to force VERSION and SUBVERS
to an empty string and use EXTRAVERSION alone to force a specific version
(could possibly be useful when bisecting from patch queues outside of Git
for example).

Makefile

@@ -105,6 +105,7 @@
 #   IGNOREGIT      : ignore GIT commit versions if set.
 #   VERSION        : force haproxy version reporting.
 #   SUBVERS        : add a sub-version (eg: platform, model, ...).
+#   EXTRAVERSION   : local version string to append (e.g. build number etc)
 #   VERDATE        : force haproxy's release date.
 #   VTEST_PROGRAM  : location of the vtest program to run reg-tests.
 #   DEBUG_USE_ABORT: use abort() for program termination, see include/haproxy/bug.h for details
@@ -451,6 +452,9 @@ ifeq ($(VERDATE),)
 VERDATE := $(shell (grep -v '^\$$Format' VERDATE 2>/dev/null || touch VERDATE) | head -n 1 | cut -f1 -d' ' | tr '-' '/')
 endif
 
+# this one is always empty by default and appended verbatim
+EXTRAVERSION =
+
 #### Build options
 # Do not change these ones, enable USE_* variables instead.
 OPTIONS_CFLAGS  =
@@ -726,8 +730,8 @@ COPTS  = -Iinclude
 COPTS += $(CFLAGS) $(TARGET_CFLAGS) $(SMALL_OPTS) $(DEFINE) $(SILENT_DEFINE)
 COPTS += $(DEBUG) $(OPTIONS_CFLAGS) $(ADDINC)
 
-ifneq ($(VERSION)$(SUBVERS),)
-COPTS += -DCONFIG_HAPROXY_VERSION=\"$(VERSION)$(SUBVERS)\"
+ifneq ($(VERSION)$(SUBVERS)$(EXTRAVERSION),)
+COPTS += -DCONFIG_HAPROXY_VERSION=\"$(VERSION)$(SUBVERS)$(EXTRAVERSION)\"
 endif
 
 ifneq ($(VERDATE),)
@@ -926,8 +930,8 @@ uninstall:
 clean:
 	$(Q)rm -f *.[oas] src/*.[oas] haproxy test .build_opts .build_opts.new
 	$(Q)for dir in . src include/* doc; do rm -f $$dir/*~ $$dir/*.rej $$dir/core; done
-	$(Q)rm -f haproxy-$(VERSION).tar.gz haproxy-$(VERSION)$(SUBVERS).tar.gz
-	$(Q)rm -f haproxy-$(VERSION) haproxy-$(VERSION)$(SUBVERS) nohup.out gmon.out
+	$(Q)rm -f haproxy-$(VERSION).tar.gz haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
+	$(Q)rm -f haproxy-$(VERSION) haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION) nohup.out gmon.out
 
 tags:
 	$(Q)find src include \( -name '*.c' -o -name '*.h' \) -print0 | \
@@ -937,17 +941,17 @@ cscope:
 	$(Q)find src include -name "*.[ch]" -print | cscope -q -b -i -
 
 tar:	clean
-	$(Q)ln -s . haproxy-$(VERSION)$(SUBVERS)
-	$(Q)tar --exclude=haproxy-$(VERSION)$(SUBVERS)/.git \
-	    --exclude=haproxy-$(VERSION)$(SUBVERS)/haproxy-$(VERSION)$(SUBVERS) \
-	    --exclude=haproxy-$(VERSION)$(SUBVERS)/haproxy-$(VERSION)$(SUBVERS).tar.gz \
-	    -cf - haproxy-$(VERSION)$(SUBVERS)/* | gzip -c9 >haproxy-$(VERSION)$(SUBVERS).tar.gz
-	$(Q)echo haproxy-$(VERSION)$(SUBVERS).tar.gz
-	$(Q)rm -f haproxy-$(VERSION)$(SUBVERS)
+	$(Q)ln -s . haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)
+	$(Q)tar --exclude=haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)/.git \
+	    --exclude=haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)/haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION) \
+	    --exclude=haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)/haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz \
+	    -cf - haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)/* | gzip -c9 >haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
+	$(Q)echo haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
+	$(Q)rm -f haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)
 
 git-tar:
-	$(Q)git archive --format=tar --prefix="haproxy-$(VERSION)$(SUBVERS)/" HEAD | gzip -9 > haproxy-$(VERSION)$(SUBVERS).tar.gz
-	$(Q)echo haproxy-$(VERSION)$(SUBVERS).tar.gz
+	$(Q)git archive --format=tar --prefix="haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION)/" HEAD | gzip -9 > haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
+	$(Q)echo haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
 
 version:
 	@echo "VERSION: $(VERSION)"