[UBSAN-MINRT] Switch to weak symbols for callbacks to allow overriding

in client code.

Author: kstoimenov

compiler-rt/lib/ubsan_minimal/ubsan_minimal_handlers.cpp

@@ -1,5 +1,6 @@
 #include "sanitizer_common/sanitizer_atomic.h"
 
+#include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>