Warn when defining a 32-bit product on a 64-bit device.

Building a 32-bit-app-only product on a 64-bit capable device is likely
to be unintentional. Print a warning if this is done implicitly,
e.g. via forgetting to define the TARGET_SUPPORTS_64_BIT_APPS variable.

Also change existing references to only treat 'true' as a positive
value, rather than all non-empty ones.

Bug: 110918674
Test: lunched 64-bit-device product that does and doesn't set this var
Change-Id: I021157c94ec3ac1c690547c8992768e58c89c287
diff --git a/core/package.mk b/core/package.mk
index f3713fc..854e009 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -8,7 +8,9 @@
 include $(BUILD_SYSTEM)/multilib.mk
 
 ifeq ($(TARGET_TRANSLATE_2ND_ARCH),true)
-  ifneq ($(TARGET_SUPPORTS_64_BIT_APPS)|$(my_module_multilib),|64)
+  ifeq ($(TARGET_SUPPORTS_64_BIT_APPS),true)
+    my_module_multilib := first
+  else ifneq ($(my_module_multilib),64)
     my_module_multilib := first
   endif
 endif