Respect user CFLAGS and LDFLAGS.

--- lpeg-1.0.2/makefile
+++ lpeg-1.0.2/makefile
@@ -1,7 +1,7 @@
 LIBNAME = lpeg
 LUADIR = ../lua/
 
-COPT = -O2 -DNDEBUG
+COPT = -DNDEBUG
 # COPT = -g
 
 CWARNS = -Wall -Wextra -pedantic \
@@ -22,7 +22,7 @@
 # -Wunreachable-code \
 
 
-CFLAGS = $(CWARNS) $(COPT) -std=c99 -I$(LUADIR) -fPIC
+CFLAGS += $(CWARNS) $(COPT) -std=c99 -I$(LUADIR) -fPIC
 CC = gcc
 
 FILES = lpvm.o lpcap.o lptree.o lpcode.o lpprint.o
@@ -36,7 +36,7 @@
 	$(MAKE) lpeg.so "DLLFLAGS = -bundle -undefined dynamic_lookup"
 
 lpeg.so: $(FILES)
-	env $(CC) $(DLLFLAGS) $(FILES) -o lpeg.so
+	env $(CC) $(DLLFLAGS) $(LDFLAGS) $(FILES) -o lpeg.so
 
 $(FILES): makefile