Export BUILDING_VENDOR_IMAGE to soong

If true, soong will autogenerate a partition module for vendor.img

Bug: 374371755
Test: verified that no vendor partition is created for aosp_x86_64
Test: verified that vendor partition is created for aosp_cf_x86_64_phone
Change-Id: I15dac7f72c2d34f928dccf5d6e4c608500c9b400
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 8c57ce6..54550d4 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -182,6 +182,7 @@
 
 $(call add_json_bool, Uml,                               $(filter true,$(TARGET_USER_MODE_LINUX)))
 $(call add_json_str,  VendorPath,                        $(TARGET_COPY_OUT_VENDOR))
+$(call add_json_bool, BuildingVendorImage,               $(BUILDING_VENDOR_IMAGE))
 $(call add_json_str,  OdmPath,                           $(TARGET_COPY_OUT_ODM))
 $(call add_json_str,  ProductPath,                       $(TARGET_COPY_OUT_PRODUCT))
 $(call add_json_str,  SystemExtPath,                     $(TARGET_COPY_OUT_SYSTEM_EXT))