libcpp: Avoid PREV_WHITE and other random content on CPP_PADDING tokens

The funlike_invocation_p macro never triggered, the other
asserts did on some tests, see below for a full list.
This seems to be caused by #pragma/_Pragma handling.
do_pragma does:
          pfile->directive_result.src_loc = pragma_token_virt_loc;
          pfile->directive_result.type = CPP_PRAGMA;
          pfile->directive_result.flags = pragma_token->flags;
          pfile->directive_result.val.pragma = p->u.ident;
when it sees a pragma, while start_directive does:
  pfile->directive_result.type = CPP_PADDING;
and so does _cpp_do__Pragma.
Now, for #pragma lex.cc will just ignore directive_result if
it has CPP_PADDING type:
              if (_cpp_handle_directive (pfile, result->flags & PREV_WHITE))
                {
                  if (pfile->directive_result.type == CPP_PADDING)
                    continue;
                  result = &pfile->directive_result;
                }
but destringize_and_run does not:
  if (pfile->directive_result.type == CPP_PRAGMA)
    {
...
    }
  else
    {
      count = 1;
      toks = XNEW (cpp_token);
      toks[0] = pfile->directive_result;
and from there it will copy type member of CPP_PADDING, but all the
other members from the last CPP_PRAGMA before it.
Small testcase for it with no option (at least no -fopenmp or -fopenmp-simd).
 #pragma GCC push_options
 #pragma GCC ignored "-Wformat"
 #pragma GCC pop_options
void
foo ()
{
  _Pragma ("omp simd")
  for (int i = 0; i < 64; i++)
    ;
}

Here is a patch that replaces those
      toks = XNEW (cpp_token);
      toks[0] = pfile->directive_result;
lines with
      toks = &pfile->avoid_paste;

2022-02-01  Jakub Jelinek  <jakub@redhat.com>

	* directives.cc (destringize_and_run): Push &pfile->avoid_paste
	instead of a copy of pfile->directive_result for the CPP_PADDING
	case.

libcpp/directives.cc

@@ -1954,8 +1954,7 @@ destringize_and_run (cpp_reader *pfile, const cpp_string *in,
   else
     {
       count = 1;
-      toks = XNEW (cpp_token);
-      toks[0] = pfile->directive_result;
+      toks = &pfile->avoid_paste;
 
       /* If we handled the entire pragma internally, make sure we get the
 	 line number correct for the next token.  */