gdb: Forward VALUE_LVAL when avoiding side effects for STRUCTOP_PTR

Assume that we have a C program like this:

  struct foo_type
  {
    int var;
  } foo;

  struct foo_type *foo_ptr = &foo;

  int
  main ()
  {
    return foo_ptr->var;
  }

Then GDB should be able to evaluate the following, however, it currently
does not:

  (gdb) start
  ...
  (gdb) whatis &(foo_ptr->var)
  Attempt to take address of value not located in memory.

The problem is that in EVAL_AVOID_SIDE_EFFECTS mode,
eval.c:evaluate_subexp_standard always returns a not_lval value as the
result for a STRUCTOP_PTR operation. As a consequence, the rest of
the code believes that one cannot take the address of the returned
value.

This patch fixes STRUCTOP_PTR handling so that the VALUE_LVAL
attribute for the returned value is properly initialized.  After this
change, the above session becomes:

  (gdb) start
  ...
  (gdb) whatis &(foo_ptr->var)
  type = int *

This commit is largely the same as commit 2520f728b710 (Forward
VALUE_LVAL when avoiding side effects for STRUCTOP_STRUCT) but applied
to STRUCTOP_PTR rather than STRUCTOP_STRUCT.  Both of these commits are
building on top of commit ac1ca910d74d (Fixes for PR exp/15364).

gdb/ChangeLog:

	* eval.c (evaluate_subexp_standard): If EVAL_AVOID_SIDE_EFFECTS
	mode, forward the VALUE_LVAL attribute to the returned value in
	the STRUCTOP_PTR case.

gdb/testsuite/ChangeLog:

	* gdb.base/whatis.c: Extend the test case.
	* gdb.base/whatis.exp: Add additional tests.

1 files changed, 4 insertions, 4 deletions

diff --git a/gdb/testsuite/gdb.base/whatis.c b/gdb/testsuite/gdb.base/whatis.c
index d60afa2..e5cfa51 100644
--- a/gdb/testsuite/gdb.base/whatis.c
+++ b/gdb/testsuite/gdb.base/whatis.c
@@ -135,7 +135,7 @@ struct t_struct {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_struct1;
+} v_struct1, *v_struct_ptr1;
 
 struct {
     char	v_char_member;
@@ -147,7 +147,7 @@ struct {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_struct2;
+} v_struct2, *v_struct_ptr2;
 
 /**** unions *******/
 
@@ -161,7 +161,7 @@ union t_union {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_union;
+} v_union, *v_union_ptr;
 
 union {
     char	v_char_member;
@@ -173,7 +173,7 @@ union {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_union2;
+} v_union2, *v_union_ptr2;
 
 /*** Functions returning type ********/