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

core/config.mk

@@ -368,10 +368,18 @@ TARGET_PREFER_32_BIT_APPS := true
 TARGET_PREFER_32_BIT_EXECUTABLES := true
 endif
 
-ifeq (,$(TARGET_SUPPORTS_32_BIT_APPS)$(TARGET_SUPPORTS_64_BIT_APPS))
+ifeq (,$(filter true,$(TARGET_SUPPORTS_32_BIT_APPS) $(TARGET_SUPPORTS_64_BIT_APPS)))
   TARGET_SUPPORTS_32_BIT_APPS := true
 endif
 
+# Sanity check to warn about likely cryptic errors later in the build.
+ifeq ($(TARGET_IS_64_BIT),true)
+  ifeq (,$(filter true false,$(TARGET_SUPPORTS_64_BIT_APPS)))
+    $(warning Building a 32-bit-app-only product on a 64-bit device. \
+      If this is intentional, set TARGET_SUPPORTS_64_BIT_APPS := false)
+  endif
+endif
+
 # "ro.product.cpu.abilist32" and "ro.product.cpu.abilist64" are
 # comma separated lists of the 32 and 64 bit ABIs (in order of
 # preference) that the target supports. If TARGET_CPU_ABI_LIST_{32,64}_BIT

core/package.mk

@@ -8,7 +8,9 @@ my_prefix := TARGET_
 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