ccan: add -Wpointer-arith and -Wwrite-strings by default

Wpointer-arith is useful for spotting GCC-isms which do arithmetic on
void pointers.  Wwrite-strings treats string constants as const char *,
which is sane (but bad for legacy code).

Makefile-ccan

@@ -3,7 +3,7 @@
 #	SRCFILES += $(wildcard ccan/*/*.c)
 
 #CCAN_CFLAGS=-g -O3 -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations
-CCAN_CFLAGS=-g -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -DCCAN_STR_DEBUG=1
+CCAN_CFLAGS=-g -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wpointer-arith -Wwrite-strings -DCCAN_STR_DEBUG=1
 CFLAGS = $(CCAN_CFLAGS) -I. $(DEPGEN) -Werror
 
 

config.h

@@ -3,7 +3,7 @@
 #define CCAN_CONFIG_H
 #define _GNU_SOURCE /* Always use GNU extensions. */
 #define CCAN_COMPILER "cc"
-#define CCAN_CFLAGS "-g -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -DCCAN_STR_DEBUG=1"
+#define CCAN_CFLAGS "-g -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wpointer-arith -Wwrite-strings -DCCAN_STR_DEBUG=1"
 
 #define HAVE_ALIGNOF 1
 #define HAVE_ASPRINTF 1