[build:Makefile] Simplify version check

Authored by: bashonly

Makefile

@@ -38,8 +38,10 @@ MANDIR ?= $(PREFIX)/man
 SHAREDIR ?= $(PREFIX)/share
 PYTHON ?= /usr/bin/env python3
 
-# $(shell) is a no-op in BSD Make and the != variable assignment operator is not supported by GNU Make <4.0
+# $(shell) and $(error) are no-ops in BSD Make and the != variable assignment operator is not supported by GNU Make <4.0
-ERROR_MSG := $(shell if [ "`echo $(MAKE_VERSION) | head -c1`" -lt "4" ] ; then echo "GNU Make 4+ or BSD Make is required" ; fi)
+VERSION_CHECK != echo supported
+VERSION_CHECK ?= $(error GNU Make 4+ or BSD Make is required)
+CHECK_VERSION := $(VERSION_CHECK)
 
 # set markdown input format to "markdown-smart" for pandoc version 2+ and to "markdown" for pandoc prior to version 2
 MARKDOWN != if [ "`pandoc -v | head -n1 | cut -d' ' -f2 | head -c1`" -ge "2" ]; then echo markdown-smart; else echo markdown; fi
@@ -76,7 +78,6 @@ offlinetest: codetest
 CODE_FOLDERS != find yt_dlp -type f -name '__init__.py' -exec dirname {} \+ | grep -v '/__' | sort
 CODE_FILES != for f in $(CODE_FOLDERS) ; do echo "$$f" | sed 's,$$,/*.py,' ; done
 yt-dlp: $(CODE_FILES)
-	@echo $(ERROR_MSG)
 	mkdir -p zip
 	for d in $(CODE_FOLDERS) ; do \
 	  mkdir -p zip/$$d ;\
@@ -109,11 +110,9 @@ supportedsites:
 	$(PYTHON) devscripts/make_supportedsites.py supportedsites.md
 
 README.txt: README.md
-	@echo $(ERROR_MSG)
 	pandoc -f $(MARKDOWN) -t plain README.md -o README.txt
 
 yt-dlp.1: README.md devscripts/prepare_manpage.py
-	@echo $(ERROR_MSG)
 	$(PYTHON) devscripts/prepare_manpage.py yt-dlp.1.temp.md
 	pandoc -s -f $(MARKDOWN) -t man yt-dlp.1.temp.md -o yt-dlp.1
 	rm -f yt-dlp.1.temp.md