[libFuzzer] Disable print_unstable_stats.test for aarch64.

[Dor1s]

Summary

Follow-up for https://reviews.llvm.org/D50264. Reported by testbots:
http://lab.llvm.org:8011/builders/clang-cmake-aarch64-full/builds/5592

[Dor1s]

Self-approval for a trivial change.

test/fuzzer/print_unstable_stats.test

+# Tests -print_unstable_stats
+UNSUPPORTED: aarch64
+
 RUN: %cpp_compiler %S/PrintUnstableStatsTest.cpp -o %t-PrintUnstableStatsTest
 
 RUN: %run %t-PrintUnstableStatsTest -print_unstable_stats=1 -runs=100000 2>&1 | FileCheck %s --check-prefix=LONG
 ; We do not observe ini functions since we take the minimum hit counts, and minimum hit counts for ini is 0.
 LONG: UNSTABLE_FUNCTIONS:
 LONG-NOT: det0()
 LONG-NOT: det1()
 LONG-NOT: det2()
 LONG-NOT: det3()
 LONG-NOT: det4()
 LONG-NOT: ini0()
 LONG-NOT: ini1()
 LONG-NOT: ini2()
 LONG-DAG: t0(int)
 LONG-DAG: t1()
 LONG-DAG: t2(int, int)
 LONG-DAG: t3()
 LONG-DAG: t4(int, int, int)
 
 LONG-DAG: stat::stability_rate: 27.59
-