[hwasan] Re-enable the test with fallback

The test passes without stdc++, but we prefer to run it with stdc++ if
availibe.

compiler-rt/test/hwasan/TestCases/sizes.cpp

@@ -1,6 +1,6 @@
 // This test requires operator new to be intercepted by the hwasan runtime,
 // so we need to avoid linking against libc++.
-// RUN: %clangxx_hwasan %s -nostdlib++ -lstdc++ -o %t
+// RUN: %clangxx_hwasan %s -nostdlib++ -lstdc++ -o %t || %clangxx_hwasan %s -o %t
 // RUN: %env_hwasan_opts=allocator_may_return_null=0 not %run %t malloc 2>&1          | FileCheck %s --check-prefix=CHECK-max
 // RUN: %env_hwasan_opts=allocator_may_return_null=1     %run %t malloc 2>&1
 // RUN: %env_hwasan_opts=allocator_may_return_null=0 not %run %t malloc max 2>&1      | FileCheck %s --check-prefix=CHECK-max
@@ -23,9 +23,6 @@
 // allocator can allocate. Tests that an integer overflow in the parameters of
 // calloc is caught.
 
-// FIXME: Fails on some bots.
-// UNSUPPORTED: target={{.*}}
-
 #include <assert.h>
 #include <malloc.h>
 #include <stdlib.h>