[pushed] Fix copy-pasto, allocate objfile_per_bfd_storage with obstack_new

[Simon Marchi <simon.marchi@polymtl.ca>]

I realized after pushing that I made a copy-pasto, I had:

  # define HAVE_IS_TRIVIALLY_COPYABLE 1

instead of

  # define HAVE_IS_TRIVIALLY_CONSTRUCTIBLE 1

with the consequence that IsMallocable was always std::true_type (and
was therefore not enforcing anything).  Fixing that mistake triggered a
build failure:

/home/simark/src/binutils-gdb/gdb/objfiles.c:150:12:   required from here
/home/simark/src/binutils-gdb/gdb/common/poison.h:228:3: error: static assertion failed: Trying to use XOBNEW with a non-POD data type.

I am not sure why I did not see this when I originally wrote the patch
(but I saw and fixed other failures).  In any case, I swapped XOBNEW
with obstack_new to get rid of it.

Regtested on the buildbot.

gdb/ChangeLog:

	* common/traits.h (HAVE_IS_TRIVIALLY_COPYABLE): Rename the wrong
	instance to...
	(HAVE_IS_TRIVIALLY_CONSTRUCTIBLE): ... this.
	* objfiles.c (get_objfile_bfd_data): Allocate
	objfile_per_bfd_storage with obstack_new when allocating on
	obstack.
---
 gdb/ChangeLog       |  9 +++++++++
 gdb/common/traits.h |  2 +-
 gdb/objfiles.c      | 10 +++++-----
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 5eb5eeaa9ad9..45e6ff719492 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2018-05-20  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* common/traits.h (HAVE_IS_TRIVIALLY_COPYABLE): Rename the wrong
+	instance to...
+	(HAVE_IS_TRIVIALLY_CONSTRUCTIBLE): ... this.
+	* objfiles.c (get_objfile_bfd_data): Allocate
+	objfile_per_bfd_storage with obstack_new when allocating on
+	obstack.
+
 2018-05-20  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* ada-lang.c (cache_symbol): Use XOBNEW and/or XOBNEWVEC and/or
diff --git a/gdb/common/traits.h b/gdb/common/traits.h
index 070ef159e5b9..e1066e0d97e5 100644
--- a/gdb/common/traits.h
+++ b/gdb/common/traits.h
@@ -38,7 +38,7 @@
    in GCC 5.  */
 #if (__has_feature(is_trivially_constructible) \
      || (defined __GNUC__ && __GNUC__ >= 5))
-# define HAVE_IS_TRIVIALLY_COPYABLE 1
+# define HAVE_IS_TRIVIALLY_CONSTRUCTIBLE 1
 #endif
 
 namespace gdb {
diff --git a/gdb/objfiles.c b/gdb/objfiles.c
index 2ec358ad4dbb..f57f4f58b008 100644
--- a/gdb/objfiles.c
+++ b/gdb/objfiles.c
@@ -144,14 +144,14 @@ get_objfile_bfd_data (struct objfile *objfile, struct bfd *abfd)
 	  storage
 	    = ((struct objfile_per_bfd_storage *)
 	       bfd_alloc (abfd, sizeof (struct objfile_per_bfd_storage)));
+	  /* objfile_per_bfd_storage is not trivially constructible, must
+	     call the ctor manually.  */
+	  storage = new (storage) objfile_per_bfd_storage ();
 	  set_bfd_data (abfd, objfiles_bfd_data, storage);
 	}
       else
-	storage = XOBNEW (&objfile->objfile_obstack, objfile_per_bfd_storage);
-
-      /* objfile_per_bfd_storage is not trivially constructible, must
-	 call the ctor manually.  */
-      storage = new (storage) objfile_per_bfd_storage ();
+	storage
+	  = obstack_new<objfile_per_bfd_storage> (&objfile->objfile_obstack);
 
       /* Look up the gdbarch associated with the BFD.  */
       if (abfd != NULL)
-- 
2.17.0