android: add function for disabling MTE at runtime

On Android, MTE is always enabled in Zygote, and is disabled after fork for apps that didn't opt-in
to MTE.

Depends on the slab canary adjustments in the previous commit.

h_malloc.c

@@ -2148,3 +2148,11 @@ COLD EXPORT int h_malloc_set_state(UNUSED void *state) {
     return -2;
 }
 #endif
+
+#ifdef __ANDROID__
+COLD EXPORT void h_malloc_disable_memory_tagging(void) {
+#ifdef HAS_ARM_MTE
+    __is_memtag_enabled = false;
+#endif
+}
+#endif

include/h_malloc.h

@@ -99,6 +99,7 @@ int h_malloc_iterate(uintptr_t base, size_t size, void (*callback)(uintptr_t ptr
               void *arg);
 void h_malloc_disable(void);
 void h_malloc_enable(void);
+void h_malloc_disable_memory_tagging(void);
 #endif
 
 // hardened_malloc extensions