testlist: Don't build sim:libcxxtest on macOS

since macOS doesn't support c++ on sim yet

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
diff --git a/testlist/sim.dat b/testlist/sim.dat
index 18a3d6d..12e9ad4 100644
--- a/testlist/sim.dat
+++ b/testlist/sim.dat
@@ -1,5 +1,6 @@
 /sim
 -Darwin,sim:cxxtest
+-Darwin,sim:libcxxtest
 
 # CONFIG_SIM_M32=y
 # The recent versions of macOS is 64-bit only