Update Makefile configuration variables.

Makefile

@@ -8,15 +8,10 @@ MAKEFLAGS += -rR
 .SUFFIXES:
 export SHELL = /bin/sh
 
-ifneq ($(findstring $(firstword $(MAKE_VERSION)),3.77 3.78 3.78.1 3.79 3.79.1 3.80),)
-$(error GNU make 3.81 or better is required)
-endif
-
 srcdir = .
 top_srcdir = .
 include $(wildcard $(top_srcdir)/Makevars.global ./Makevars.local)
 
-
 # info: src/stub needs special build tools from https://github.com/upx/upx-stubtools
 BUILD_STUB = 0
 ifneq ($(wildcard $(HOME)/local/bin/bin-upx/upx-stubtools-check-version),)
@@ -26,7 +21,6 @@ ifneq ($(wildcard $(HOME)/bin/bin-upx/upx-stubtools-check-version),)
 BUILD_STUB = 1
 endif
 
-
 default:
 	@echo "UPX info: please choose a target for 'make'"
 
@@ -37,7 +31,6 @@ endif
 	$(MAKE) -C src $@
 	$(MAKE) -C doc $@
 
-
 .PHONY: default all mostlyclean clean distclean maintainer-clean
 
 # vim:set ts=8 sw=8 noet: