[SVE] Add a couple of extra sizeless type tests

[rsandifo-arm]

Summary

This patch adds tests for things that happened to be fixed by previous
patches, but that should continue working if we do decide to treat
sizeless types as incomplete types.

[efriedma]

LGTM

clang/test/Sema/sizeless-1.c

void test_generic(void) {
   svint8_t local_int8;
   svint16_t local_int16;
 
   int a1[_Generic(local_int8, svint8_t : 1, svint16_t : 2, default : 3) == 1 ? 1 : -1];
   int a2[_Generic(local_int16, svint8_t : 1, svint16_t : 2, default : 3) == 2 ? 1 : -1];
   int a3[_Generic(0, svint8_t : 1, svint16_t : 2, default : 3) == 3 ? 1 : -1];
   (void)_Generic(0, svint8_t : 1, svint8_t : 2, default : 3); // expected-error {{type 'svint8_t' (aka '__SVInt8_t') in generic association compatible with previously specified type 'svint8_t'}} expected-note {{compatible type}}
 }
+
+void test_compound_literal(void) {
+  svint8_t local_int8;
+
+  (void)(svint8_t){local_int8};
+}
 #endif

clang/test/SemaCXX/sizeless-1.cpp

 
 #if __cplusplus >= 201103L
 template <typename T>
 using array_alias = T[1]; // expected-error {{array has sizeless element type '__SVInt8_t'}}
 extern array_alias<int> *array_alias_int_ptr;
 extern array_alias<svint8_t> *array_alias_int8_ptr; // expected-note {{in instantiation of template type alias 'array_alias' requested here}}
 #endif
 
+extern "C" svint8_t c_return_int8();
+
 void cxx_only(int sel) {
   svint8_t local_int8;
   svint16_t local_int16;
 
   pass_int8_ref(local_int8);
   pass_int8_ref(local_int16); // expected-error {{no matching function}}
 
   local_int8 = return_int8_ref();