Privory uses STRIP Makefile variable for passing strip argument,
this clashes with STRIP set in the environment. So rename STRIP ->
STRIP_ARGS and then use real STRIP instead of STRIP_PROG with
fallback on predefined "strip" if STRIP is not set.

--- privoxy-3.0.28-stable/GNUmakefile.in.orig	2020-08-19 15:24:46.930551734 +0300
+++ privoxy-3.0.28-stable/GNUmakefile.in	2020-08-19 16:12:18.214837417 +0300
@@ -117,7 +117,7 @@
 CP         = cp -f
 RMDIR      = rmdir
 MKDIR      = ./mkinstalldirs
-STRIP_PROG = strip
+STRIP     ?= strip
 SED        = sed
 GREP       = grep
 CAT        = cat
@@ -391,7 +391,7 @@
 	@$(ECHO) "You have run autoconf && autoheader && ./configure right?"
 	@$(ECHO) ""
 	$(MAKE) $(PROGRAM)
-	$(STRIP_PROG) $(PROGRAM)
+	$(STRIP) $(PROGRAM)
 	$(LN) -s `pwd` ../privoxy-$(VERSION)-$(CODE_STATUS)
 # add program
 	(cd .. && $(TAR) --exclude "PACKAGERS" -cvhf $(GEN_DIST_TAR_NAME) privoxy-$(VERSION)-$(CODE_STATUS)/$(PROGRAM))
@@ -822,7 +822,7 @@
 	 fi)
 
 install-strip:
-	$(MAKE) install STRIP=-s
+	$(MAKE) install STRIP_ARG=-s
 
 # FIXME: Test USER and GROUP on Slack to make sure this works as
 # intended.
@@ -848,10 +848,10 @@
 		$(DESTDIR)$(CONF_DEST)/templates $(DESTDIR)$(SHARE_DEST) \
 		$(DESTDIR)$(LOG_DEST) $(DESTDIR)$(PID_DEST)
 	@# Install the executable binary, strip if invoked as install-strip
-	@test -n "$(STRIP)" &&\
+	@test -n "$(STRIP_ARG)" &&\
 	$(ECHO) Installing $(PROGRAM) stripped executable to $(SBIN_DEST) ||\
 	$(ECHO) Installing $(PROGRAM) executable to $(DESTDIR)$(SBIN_DEST)
-	$(INSTALL) $(INSTALL_P) $(STRIP) $(PROGRAM) $(DESTDIR)$(SBIN_DEST)
+	$(INSTALL) $(INSTALL_P) $(STRIP_ARG) $(PROGRAM) $(DESTDIR)$(SBIN_DEST)
 
 	@# Install the DOCS and man page. install-sh only does one file at a time.
 	@# FIXME: only handles jpegs.