Extend sizeof check to incomplete enums and unions

And produce gcc-like error message.

Author: petr-bauch

regression/cbmc/incomplete-sizeof-enum/main.c

@@ -0,0 +1,10 @@
+#include <assert.h>
+#include <stdlib.h>
+
+enum foo;
+
+int main(int argc, char **argv)
+{
+  size_t s = sizeof(enum foo);
+  assert(s == 0);
+}

regression/cbmc/incomplete-sizeof-enum/test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+
+^EXIT=6$
+^SIGNAL=0$
+^file main.c line \d+ function main: invalid application of \'sizeof\' to an incomplete type$
+^CONVERSION ERROR$
+--
+^warning: ignoring

regression/cbmc/incomplete-sizeof/main.c renamed to regression/cbmc/incomplete-sizeof-struct/main.c

@@ -0,0 +1,9 @@
+CORE
+main.c
+
+^EXIT=6$
+^SIGNAL=0$
+^file main.c line \d+ function main: invalid application of \'sizeof\' to an incomplete type$
+^CONVERSION ERROR$
+--
+^warning: ignoring

regression/cbmc/incomplete-sizeof-struct/test.desc

@@ -0,0 +1,10 @@
+#include <assert.h>
+#include <stdlib.h>
+
+union foo;
+
+int main(int argc, char **argv)
+{
+  size_t s = sizeof(union foo);
+  assert(s == 0);
+}

regression/cbmc/incomplete-sizeof-union/main.c

@@ -0,0 +1,9 @@
+CORE
+main.c
+
+^EXIT=6$
+^SIGNAL=0$
+^file main.c line \d+ function main: invalid application of \'sizeof\' to an incomplete type$
+^CONVERSION ERROR$
+--
+^warning: ignoring

regression/cbmc/incomplete-sizeof-union/test.desc

@@ -952,12 +952,15 @@ void c_typecheck_baset::typecheck_expr_sizeof(exprt &expr)
   else
   {
     if(
-      type.id() == ID_struct_tag &&
-      to_struct_type(follow_tag(to_struct_tag_type(type))).is_incomplete())
+      (type.id() == ID_struct_tag &&
+       to_struct_type(follow_tag(to_struct_tag_type(type))).is_incomplete()) ||
+      (type.id() == ID_union_tag &&
+       to_union_type(follow_tag(to_union_tag_type(type))).is_incomplete()) ||
+      (type.id() == ID_c_enum && to_c_enum_type(type).is_incomplete()))
     {
       error().source_location = expr.source_location();
-      error() << "calling sizeof for incomplete type: " << to_string(type)
-              << eom;
+      error() << "invalid application of \'sizeof\' to an incomplete type\n\t\'"
+              << to_string(type) << "\'" << eom;
       throw 0;
     }