Fixes clang build

--- Makefile.orig	2015-03-21 06:43:07 UTC
+++ Makefile
@@ -56,8 +56,8 @@
 #FLAGS = -O -m -DMEM_CHECK
 
 # for gcc
-CC = gcc
-FLAGS = -O3 -W -Wall -ansi
+CC ?= cc
+FLAGS = -ansi -DAUDIT -DMEM_DEBUG
 #FLAGS = -g -W -Wall -ansi -DAUDIT -DMEM_DEBUG
 #FLAGS = -O3 -mcpu=pentiumpro -fomit-frame-pointer -W -Wall -ansi -DMEM_CHECK
 #FLAGS = -O -pg -W -Wall -ansi -DMEM_CHECK
@@ -88,7 +88,7 @@ endif
 # ----- nothing should be changed below this line -----
 
 COBJ = mem.o nhash.o cpp.o lexer.o assert.o macro.o eval.o
-CFLAGS = $(FLAGS)
+CFLAGS += $(FLAGS)
 
 all: ucpp
 	@ar cq libucpp.a *.o