[libcxx] <experimental/simd> excluded long double for 32-bits x86 temporarily

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D159514

NOKEYCHECK=True
GitOrigin-RevId: 81a3828dbd992aaf03cb6080abace8114ba40f8e

Author: joy2myself

test/std/experimental/simd/test_utils.h

@@ -40,8 +40,8 @@ struct TestAllSimdAbiFunctor {
   }
 };
 
-// TODO: Support long double (12 bytes) for MinGW (DLL, i686)
-#ifdef __MINGW32__
+// TODO: Support long double (12 bytes) for 32-bits x86
+#ifdef __i386__
 using arithmetic_no_bool_types = types::concatenate_t<types::integer_types, types::type_list<float, double>>;
 #else
 using arithmetic_no_bool_types = types::concatenate_t<types::integer_types, types::floating_point_types>;