Refactor Bison installation in Makefile

Updated Bison download URL to use a variable for versioning.

Author: HofiOne

Makefile

@@ -2,6 +2,10 @@ ROOT_DIR=$(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
 SOURCEDIRS=$(ROOT_DIR)/syslog_ng_cfg_helper $(ROOT_DIR)/tests
 
 BISON_INSTALL_PATH := /usr/local
+BISON_VERSION := 3.7.6
+# the "official" gnu source - https://ftp.gnu.org/gnu/bison//bison-${BISON_VERSION}.tar.gz - fails more and more, use our mirror
+BISON_DNLD_URL := https://github.com/syslog-ng/syslog-ng-deps/raw/refs/heads/main/bison/$(BISON_VERSION)/bison.tar.gz
+
 
 SYSLOG_NG_VERSION := 4.8.1
 SYSLOG_NG_RELEASE_URL := https://github.com/syslog-ng/syslog-ng/releases/tag/syslog-ng-$(SYSLOG_NG_VERSION)
@@ -13,11 +17,7 @@ SYSLOG_NG_WORKING_DIR := $(WORKING_DIR)/syslog-ng-source
 SYSLOG_NG_TARBALL := $(WORKING_DIR)/syslog-ng.tar.gz
 
 bison:
-	BISON_VERSION=3.7.6
-	# the "official" gnu source - https://ftp.gnu.org/gnu/bison//bison-${BISON_VERSION}.tar.gz - fails more and more, use our mirror
-	URL=https://github.com/syslog-ng/syslog-ng-deps/raw/refs/heads/main/bison/$(BISON_VERSION)/bison.tar.gz
-
-	wget $(URL) -O /tmp/bison.tar.gz
+	wget $(BISON_DNLD_URL) -O /tmp/bison.tar.gz
 	tar -xzf /tmp/bison.tar.gz -C /tmp
 	cd /tmp/bison-$(BISON_VERSION) && ./configure --prefix=$(BISON_INSTALL_PATH) --disable-nls && make -j && make install