Add commented-out build options to Makefile for run-time checks.

Makefile

@@ -1,6 +1,10 @@
 CC=gcc
-CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas
+CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual
 LDFLAGS=
+# CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -g -fsanitize=thread
+# LDFLAGS=-g -fsanitize=thread
+# CFLAGS=-O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -g -fsanitize=address
+# LDFLAGS=-g -fsanitize=address
 LIBS=-lm -lpthread -lz
 ZOPFLI=zopfli/src/zopfli/
 ZOP=deflate.o blocksplitter.o tree.o lz77.o cache.o hash.o util.o squeeze.o katajainen.o symbols.o