Fix __func__, __FUNCTION__ and __PRETTY_FUNCTION__ section allocations so they can be moved into irom0.text.
Restores changed behaviour from GCC commit c3a961ad27fc21a3af847693820fa9c04dd00940.

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b57ded813b6..8566fb4cd0f 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4495,8 +4495,7 @@ cp_make_fname_decl (location_t loc, tree id, int type_dep)
 
   if (init)
     {
-      SET_DECL_VALUE_EXPR (decl, init);
-      DECL_HAS_VALUE_EXPR_P (decl) = 1;
+      DECL_INITIAL (decl) = init;
       /* For decl_constant_var_p.  */
       DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = 1;
     }