[compiler-rt][asan] Re-enable ManyThreadsTest on AArch64 (#127795)

Disabled in 2ab51bf13a, doesn't hang for
me on AArch64 (Graviton 3, tested 1000 iterations). May still be an
issue, but hard to know unless we enable it again to find out.

n.b. test was also disabled on PowerPC in
467afc5f84 for same reason and it has also
been observed on x86:
https://lists.llvm.org/pipermail/llvm-dev/2016-January/094607.html

Fixes: https://github.com/llvm/llvm-project/issues/24763

compiler-rt/lib/asan/tests/asan_test.cpp

@@ -369,8 +369,7 @@ void *ManyThreadsWorker(void *a) {
   return 0;
 }
 
-#if !defined(__aarch64__) && !defined(__powerpc64__)
-// FIXME: Infinite loop in AArch64 (PR24389).
+#if !defined(__powerpc64__)
 // FIXME: Also occasional hang on powerpc.  Maybe same problem as on AArch64?
 TEST(AddressSanitizer, ManyThreadsTest) {
   const size_t kNumThreads =