Remove compatibility_matrix.9.xml from 'next' builds

This compatibility matrix has not be finalized or released yet, so it's
very important that releasing devices in the 'next' configuration don't
use its contents.

Test: m
Bug: 296930312
Change-Id: I843a24308a1653bff0b4842ff71e657304bea2c8
Merged-In: I843a24308a1653bff0b4842ff71e657304bea2c8
diff --git a/compatibility_matrices/Android.mk b/compatibility_matrices/Android.mk
index d356cf3..c2ffb84 100644
--- a/compatibility_matrices/Android.mk
+++ b/compatibility_matrices/Android.mk
@@ -106,9 +106,15 @@
     framework_compatibility_matrix.6.xml \
     framework_compatibility_matrix.7.xml \
     framework_compatibility_matrix.8.xml \
-    framework_compatibility_matrix.9.xml \
     framework_compatibility_matrix.device.xml \
 
+# Only allow the use of the unreleased compatibility matrix when we can use unfrozen
+# interfaces (in the `next` release configuration).
+ifeq ($(RELEASE_AIDL_USE_UNFROZEN),true)
+my_system_matrix_deps += \
+    framework_compatibility_matrix.9.xml
+endif
+
 my_framework_matrix_deps += \
     $(my_system_matrix_deps)