[ubsan] Properly create const char type

[Marek Polacek]

I was creating the const char type in a wrong way.  I should've used
build_qualified_type, otherwise we'd ICE in the C++ FE later on due to
mismatched TYPE_CANONICALs...

Tested x86_64-pc-linux-gnu, applying to ubsan branch.

2013-08-05  Marek Polacek  <pola...@redhat.com>

        * ubsan.c (ubsan_source_location_type): Properly create
        const char type using build_qualified_type.

        * c-c++-common/ubsan/const-char-1.c: New test.

--- gcc/ubsan.c.mp      2013-08-05 16:15:03.769489097 +0200
+++ gcc/ubsan.c 2013-08-05 16:15:12.352528297 +0200
@@ -226,8 +226,8 @@ ubsan_source_location_type (void)
   static const char *field_names[3]
     = { "__filename", "__line", "__column" };
   tree fields[3], ret;
-  tree const_char_type = char_type_node;
-  TYPE_READONLY (const_char_type) = 1;
+  tree const_char_type = build_qualified_type (char_type_node,
+                                              TYPE_QUAL_CONST);
 
   ret = make_node (RECORD_TYPE);
   for (int i = 0; i < 3; i++)
--- gcc/testsuite/c-c++-common/ubsan/const-char-1.c.mp  2013-08-05 
16:15:48.733686613 +0200
+++ gcc/testsuite/c-c++-common/ubsan/const-char-1.c     2013-08-05 
16:18:06.384287418 +0200
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=shift" } */
+
+void
+foo (void)
+{
+  int y = 1 << 2;
+  __builtin_printf ("%d\n", y);
+}

        Marek