Wrap BFD headers in extern "C"

Wrap BFD headers in extern "C"

These were the BFD changes needed for building a C++ GDB with
--enable-targets=all, on x86_64 Fedora 20.

For libbfd.h and libcoff.h, this does same as already done when
generating bfd.h: open extern "C" in the -in.h header, and close it
from the Makefile.

bfd/doc/ChangeLog:
2015-02-11  Pedro Alves  <palves@redhat.com>

	* Makefile.am (libbfd.h, libcoff.h): Close extern "C" scope.
	* Makefile.in: Regenerate.

bfd/ChangeLog:
2015-02-11  Pedro Alves  <palves@redhat.com>

	* libbfd-in.h [__cplusplus]: Open extern "C" scope.
	* libcoff-in.h [__cplusplus]: Open extern "C" scope.
	* libbfd.h: Regenerate.
	* libcoff.h: Regenerate.

	* elf-bfd.h [__cplusplus]: Wrap in extern "C".
	* mach-o.h [__cplusplus]: Wrap in extern "C".
	* som.h [__cplusplus]: Wrap in extern "C".