[libcxxabi] Stub out 'sleep' call when _LIBCXXABI_HAS_NO_THREADS is defined.

While running this test on a bare metal target, I got an error as 'sleep' was not available on that system. As 'sleep' call is not doing anything useful for cases when _LIBCXXABI_HAS_NO_THREADS is defined. This patch puts it under this check.

Reviewed By: ldionne

Differential Revision: https://reviews.llvm.org/D89871

GitOrigin-RevId: 272279a1c0fa4142e599aecdc75ef68720a81607
diff --git a/test/test_exception_storage.pass.cpp b/test/test_exception_storage.pass.cpp
index 5c29c45..bf42366 100644
--- a/test/test_exception_storage.pass.cpp
+++ b/test/test_exception_storage.pass.cpp
@@ -29,7 +29,9 @@
         std::printf("Got different globals!\n");
 
     *result = (size_t) glob1;
+#ifndef _LIBCXXABI_HAS_NO_THREADS
     sleep ( 1 );
+#endif
     return parm;
 }