ld.so: Replace DL_RO_DYN_SECTION with dl_relocate_ld [BZ #28340]

We can't relocate entries in dynamic section if it is readonly:

1. Add a l_ld_readonly field to struct link_map to indicate if dynamic
section is readonly and set it based on p_flags of PT_DYNAMIC segment.
2. Replace DL_RO_DYN_SECTION with dl_relocate_ld to decide if dynamic
section should be relocated.
3. Remove DL_RO_DYN_TEMP_CNT.
4. Don't use a static dynamic section to make readonly dynamic section
in vDSO writable.
5. Remove the temp argument from elf_get_dynamic_info.

This fixes BZ #28340.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

include/link.h

@@ -205,6 +205,7 @@ struct link_map
     unsigned int l_free_initfini:1; /* Nonzero if l_initfini can be
 				       freed, ie. not allocated with
 				       the dummy malloc in ld.so.  */
+    unsigned int l_ld_readonly:1; /* Nonzero if dynamic section is readonly.  */
 
     /* NODELETE status of the map.  Only valid for maps of type
        lt_loaded.  Lazy binding sets l_nodelete_active directly,
@@ -342,6 +343,8 @@ struct link_map
     unsigned long long int l_serial;
   };
 
+#include <dl-relocate-ld.h>
+
 /* Information used by audit modules.  For most link maps, this data
    immediate follows the link map in memory.  For the dynamic linker,
    it is allocated separately.  See link_map_audit_state in