bootstrap: Fix building with GCC 4.2 [PR89494]

GCC 4.2 (but I think not the latest tip of GCC 4.2 branch) has broken value
initialization, see PR33916.  The following patch provides a workaround for
that.  Tested with GCC 4.2 on a reduced testcase I've distilled from the
assign_param_data_one class which has been miscompiled the same.

2020-04-16  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/89494
	* function.c (assign_parm_find_data_types): Add workaround for
	BROKEN_VALUE_INITIALIZATION compilers.

gcc/ChangeLog

+2020-04-16  Jakub Jelinek  <jakub@redhat.com>
+
+	PR bootstrap/89494
+	* function.c (assign_parm_find_data_types): Add workaround for
+	BROKEN_VALUE_INITIALIZATION compilers.
+
 2020-04-16  Richard Biener  <rguenther@suse.de>
 
 	* gdbhooks.py (TreePrinter): Print SSA_NAME_VERSION of SSA_NAME

gcc/function.c

@@ -2414,7 +2414,15 @@ assign_parm_find_data_types (struct assign_parm_data_all *all, tree parm,
 {
   int unsignedp;
 
+#ifndef BROKEN_VALUE_INITIALIZATION
   *data = assign_parm_data_one ();
+#else
+  /* Old versions of GCC used to miscompile the above by only initializing
+     the members with explicit constructors and copying garbage
+     to the other members.  */
+  assign_parm_data_one zero_data = {};
+  *data = zero_data;
+#endif
 
   /* NAMED_ARG is a misnomer.  We really mean 'non-variadic'. */
   if (!cfun->stdarg)