It's not pretty, but the following patch fixes the x32 build:
--- abseil-20260526.0/debian/rules	2026-07-14 01:24:45.000000000 +0300
+++ abseil-20260526.0/debian/rules	2026-07-19 14:18:20.000000000 +0300
@@ -66,7 +66,8 @@
   TEST_EXCLUSIONS += absl_waiter_test

 else ifneq (,$(filter x32,$(DEB_HOST_ARCH)))
-  TEST_EXCLUSIONS += absl_hash_instantiated_test
+  export DEB_CXXFLAGS_MAINT_APPEND += -Os
+  TEST_EXCLUSIONS += absl_raw_hash_set_test absl_symbolize_test absl_mutex_test absl_notification_test absl_per_thread_sem_test absl_waiter_test absl_clock_interface_test
 endif

 ifneq (,$(TEST_EXCLUSIONS))