dump-c: when removing const-ness, also handle bit fields

regression/goto-instrument/chain.sh

@@ -38,6 +38,7 @@ elif echo $args | grep -q -- "--dump-c-type-header" ; then
   cat "${name}-mod.gb"
   mv "${name}.gb" "${name}-mod.gb"
 elif echo $args | grep -q -- "--dump-c" ; then
+  cat "${name}-mod.gb"
   mv "${name}-mod.gb" "${name}-mod.c"
 
   if [[ "${is_windows}" == "true" ]]; then

regression/goto-instrument/dump-decl-const/main.c

@@ -0,0 +1,19 @@
+#include <assert.h>
+
+struct S
+{
+  const int x;
+  const int y : 8;
+  const int *const p;
+};
+
+int foo()
+{
+  return 1;
+}
+
+int main()
+{
+  struct S s1 = {foo(), 1, 0};
+  assert(s1.x == 1);
+}

regression/goto-instrument/dump-decl-const/test.desc

@@ -0,0 +1,16 @@
+CORE
+main.c
+--dump-c
+signed int x
+signed int y
+const signed int \*p
+^[[:space:]]*s1 = \(struct S\)\{ .* \};
+^EXIT=0$
+^SIGNAL=0$
+--
+const signed int x
+const signed int y
+const p
+--
+This test demonstrates that the constness of struct members has been removed,
+which is necessary as the initialisation is not performed in the declaration.

src/goto-instrument/goto_program2code.cpp

@@ -1591,6 +1591,8 @@ void goto_program2codet::remove_const(typet &type)
         ++it)
       remove_const(it->type());
   }
+  else if(type.id() == ID_c_bit_field)
+    to_c_bit_field_type(type).subtype().remove(ID_C_constant);
 }
 
 static bool has_labels(const codet &code)