Parse RELEASE_PLATFORM_BASE_SDK_EXTENSION_VERSION

Fall back to PLATFORM_SDK_EXTENSION_VERSION if value is not set

Bug: 375152642
Test: m sdk dist && unzip -p out/dist/android-sdk_linux-x86-*.zip android-sdk_linux-x86/samples/android-*/source.properties
Verify that isBaseSdk is still true when flag is undefined.

Change-Id: Id454176ef4146c9317a84161b5370b91e7e205e4
diff --git a/core/version_util.mk b/core/version_util.mk
index 0e34634..2bf41ec 100644
--- a/core/version_util.mk
+++ b/core/version_util.mk
@@ -23,6 +23,7 @@
 #     PLATFORM_DISPLAY_VERSION
 #     PLATFORM_SDK_VERSION
 #     PLATFORM_SDK_EXTENSION_VERSION
+#     PLATFORM_BASE_SDK_EXTENSION_VERSION
 #     PLATFORM_VERSION_CODENAME
 #     DEFAULT_APP_TARGET_SDK
 #     BUILD_ID
@@ -67,8 +68,16 @@
 PLATFORM_SDK_EXTENSION_VERSION := $(RELEASE_PLATFORM_SDK_EXTENSION_VERSION)
 .KATI_READONLY := PLATFORM_SDK_EXTENSION_VERSION
 
-# This is the sdk extension version that PLATFORM_SDK_VERSION ships with.
-PLATFORM_BASE_SDK_EXTENSION_VERSION := $(PLATFORM_SDK_EXTENSION_VERSION)
+ifdef PLATFORM_BASE_SDK_EXTENSION_VERSION
+  $(error Do not set PLATFORM_BASE_SDK_EXTENSION_VERSION directly. Use RELEASE_PLATFORM_BASE_SDK_EXTENSION_VERSION. value: $(PLATFORM_BASE_SDK_EXTENSION_VERSION))
+endif
+ifdef RELEASE_PLATFORM_BASE_SDK_EXTENSION_VERSION
+  # This is the sdk extension version that PLATFORM_SDK_VERSION ships with.
+  PLATFORM_BASE_SDK_EXTENSION_VERSION := $(RELEASE_PLATFORM_BASE_SDK_EXTENSION_VERSION)
+else
+  # Fallback to PLATFORM_SDK_EXTENSION_VERSION if RELEASE_PLATFORM_BASE_SDK_EXTENSION_VERSION is undefined.
+  PLATFORM_BASE_SDK_EXTENSION_VERSION := $(PLATFORM_SDK_EXTENSION_VERSION)
+endif
 .KATI_READONLY := PLATFORM_BASE_SDK_EXTENSION_VERSION
 
 ifdef PLATFORM_VERSION_CODENAME