[GOLD] PR27815, gold fails to build with latest GCC

...gold/gc.h:250:37: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: [-Werror]
  250 |                 (*secvec).push_back(Section_id(NULL, 0));
      |                                     ^~~~~~~~~~~~~~~~~~~

	PR gold/27815
	* gc.h (gc_process_relocs): Use nullptr in Section_id constructor.

Don't use nullptr, it requires -std=c++11 on versions of gcc prior to
6.1.  It would be possible to arrange to pass -std=c++11 automatically
when required (top level configure does that for gcc builds) but that
seems overkill and since we're not up-to-date on the top level config
files would mean someone would need to sync those over.

	PR gold/27815
	* gc.h (gc_process_relocs): Use cast in Section_id constructor.

https://en.cppreference.com/w/cpp/types/NULL says NULL might be
defined as nullptr.
https://en.cppreference.com/w/cpp/language/reinterpret_cast says
reinterpret_cast can't be used on nullptr.

	PR gold/28106
	PR gold/27815
	* gc.h (gc_process_relocs): Use static_cast in Section_id constructor.

(cherry picked from commit 1f1fb219fdc4f96fd967e6173e9090c4c4917e96)
(cherry picked from commit 5d7f11f0e76ca290e3745c8836b92a5266cb84e2)
(cherry picked from commit b97bd976233ee4d43c2fe18f6356e62779cbe82d)

diff --git a/gold/gc.h b/gold/gc.h
index 2c20b44b6ede2fa4b5357af20e795462bbf19659..4a1368f5abe4d54171de76e31df574477a504916 100644 (file)
--- a/gold/gc.h
+++ b/gold/gc.h
@@ -247,7 +247,7 @@ gc_process_relocs(
              if (is_ordinary) 
                (*secvec).push_back(Section_id(src_obj, dst_indx));
              else
-                (*secvec).push_back(Section_id(NULL, 0));
+               (*secvec).push_back(Section_id(static_cast<Relobj*>(NULL), 0));
               // If the target of the relocation is an STT_SECTION symbol,
               // make a note of that by storing -1 in the symbol vector.
               if (lsym.get_st_type() == elfcpp::STT_SECTION)
@@ -329,7 +329,7 @@ gc_process_relocs(
               if (is_ordinary && dst_obj != NULL)
                (*secvec).push_back(Section_id(dst_obj, dst_indx));
              else
-                (*secvec).push_back(Section_id(NULL, 0));
+               (*secvec).push_back(Section_id(static_cast<Relobj*>(NULL), 0));
               (*symvec).push_back(gsym);
              (*addendvec).push_back(std::make_pair(
                                        static_cast<long long>(symvalue),