c++: Fix handling of internal fn calls in statement expressions [PR94385]

c++: Fix handling of internal fn calls in statement expressions [PR94385]

The following testcase ICEs, because the FE when processing the statement
expression changes the .VEC_CONVERT internal fn CALL_EXPR into .PHI call.
That is because the internal fn call is recorded in the base.u.ifn
field, which overlaps base.u.bits.lang_flag_1 which is used for
STMT_IS_FULL_EXPR_P, so this essentially does ifn |= 2 on little-endian.
STMT_IS_FULL_EXPR_P bit is used in:
cp-gimplify.c-  if (STATEMENT_CODE_P (code))
cp-gimplify.c-    {
cp-gimplify.c-      saved_stmts_are_full_exprs_p = stmts_are_full_exprs_p ();
cp-gimplify.c-      current_stmt_tree ()->stmts_are_full_exprs_p
cp-gimplify.c:        = STMT_IS_FULL_EXPR_P (*expr_p);
cp-gimplify.c-    }
and
pt.c-  if (STATEMENT_CODE_P (TREE_CODE (t)))
pt.c:    current_stmt_tree ()->stmts_are_full_exprs_p = STMT_IS_FULL_EXPR_P (t);
so besides being wrong on some other codes, it actually isn't beneficial at
all to set it on anything else, so the following patch restricts it to
trees with STATEMENT_CODE_P TREE_CODE.

2020-03-30  Jakub Jelinek  <jakub@redhat.com>

	PR c++/94385
	* semantics.c (add_stmt): Only set STMT_IS_FULL_EXPR_P on trees with
	STATEMENT_CODE_P code.

	* c-c++-common/pr94385.c: New test.