s390: avoid peeking eof after __vector

Same like PR101168, it is need for s390 to
avoid peeking eof after vector keyword.
And similar test case is also ok for s390.

	PR target/95782

gcc/ChangeLog:

	* config/s390/s390-c.cc (s390_macro_to_expand): Avoid empty identifier.

gcc/testsuite/ChangeLog:

	* g++.target/s390/pr95782.C: New test.

gcc/config/s390/s390-c.cc

@@ -275,7 +275,9 @@ s390_macro_to_expand (cpp_reader *pfile, const cpp_token *tok)
       /* __vector long __bool a; */
       if (ident == C_CPP_HASHNODE (__bool_keyword))
 	expand_bool_p = true;
-      else
+
+      /* If there are more tokens to check.  */
+      else if (ident)
 	{
 	  /* Triggered with: __vector long long __bool a; */
 	  do

gcc/testsuite/g++.target/s390/pr95782.C

@@ -0,0 +1,5 @@
+// { dg-do compile }
+// { dg-options "-march=z14 -mzvector" }
+
+using vdbl =  __vector double;
+#define BREAK 1