Don't allow int<->pointer conversions.

Normally we don't have -Werror for upstream code, but for those warnings
that probably point to 32-bit assumptions about pointers, we want those
warnings to always be errors.

Change-Id: Ibece9caf09b2f7989ca600ef448d07868669a8fb

libc/Android.mk

@@ -562,7 +562,13 @@ libc_common_cflags := \
     -DINET6 \
     -I$(LOCAL_PATH)/private \
     -DPOSIX_MISTAKE \
-    -Wall -Wextra
+    -Wall -Wextra \
+
+# Try to catch typical 32-bit assumptions that break with 64-bit pointers.
+libc_common_cflags += \
+    -Werror=pointer-to-int-cast \
+    -Werror=int-to-pointer-cast \
+    -Werror=type-limits \
 
 ifeq ($(strip $(DEBUG_BIONIC_LIBC)),true)
   libc_common_cflags += -DDEBUG