Make "disable memory mitigations" and "set heap tagging level" more available.

These were only available internally via android_mallopt(), but they're
likely to be needed by more code in future, so move them into mallopt().

This change leaves the android_mallopt() options for now, but I plan on
coming back to remove them after I've switched the handful of callers
over to mallopt() instead.

Bug: http://b/135772972
Test: treehugger
Change-Id: Ia154614069a7623c6aca85975a91e6a156f04759
diff --git a/libc/bionic/memory_mitigation_state.h b/libc/bionic/memory_mitigation_state.h
index ffa1912..047b6ad 100644
--- a/libc/bionic/memory_mitigation_state.h
+++ b/libc/bionic/memory_mitigation_state.h
@@ -30,4 +30,4 @@
 
 #include <stddef.h>
 
-bool DisableMemoryMitigations(void* arg, size_t arg_size);
+bool DisableMemoryMitigations(int arg);