don't set ${PREFIX} here because this confuses the fake installation

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -28,8 +28,8 @@
 # SPDX-FileCopyrightText:  © 2020 David Wicksell <dlw@linux.com>
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-CC       := gcc
-CFLAGS   := -std=gnu99 -Wall -Wextra -fsigned-char -fwrapv
+CC       ?= gcc
+CFLAGS   += -std=gnu99 -Wall -Wextra -fsigned-char -fwrapv
 CPPFLAGS := -Iinclude
 LDLIBS   := -lcrypt -lm
 PROG     := rsm
@@ -41,7 +41,7 @@ DOCS     := doc/adoc/*.adoc
 MAN      := doc/man/rsm.1
 RM       := rm -f
 GZIP     := gzip -f9
-PREFIX   := /usr/local
+#PREFIX   := /usr/local
 OS       != uname
 GIT_SHA  != git rev-parse --short=10 HEAD 2>/dev/null; true
 
@@ -63,7 +63,6 @@ GIT_SHA  != git rev-parse --short=10 HEAD 2>/dev/null;
 .       endif
 .   endif
 .else
-    CFLAGS   += -O3
     CPPFLAGS += -DNDEBUG
 .endif
 
@@ -96,10 +95,6 @@ clean:
 
 .PHONY: install
 install: $(PROG)
-	@if [ "$${USER}" != "root" ]; then \
-	    echo "You must install $(PROG) and $(UTILS) as root"; \
-	    exit 1; \
-	else \
 	    echo install -d -o 0 -g 0 -m 755 $(PREFIX)/bin; \
 	    install -d -o 0 -g 0 -m 755 $(PREFIX)/bin; \
 	    echo install -o 0 -g 0 -m 755 -s $(PROG) $(PREFIX)/bin; \
@@ -108,7 +103,6 @@ install: $(PROG)
 	    install -d -o 0 -g 0 -m 755 $(PREFIX)/share/rsm; \
 	    echo install -o 0 -g 0 -m 644 $(UTILS) $(PREFIX)/share/rsm; \
 	    install -o 0 -g 0 -m 644 $(UTILS) $(PREFIX)/share/rsm; \
-	fi
 
 .PHONY: uninstall
 uninstall:
