[binutils-gdb] Default initialize enum flags to 0

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 1b90b1390679473dd84416e462afa1587769ceec ***

Author: Simon Marchi <simon.marchi@ericsson.com>
Branch: master
Commit: 1b90b1390679473dd84416e462afa1587769ceec

Default initialize enum flags to 0

... so that we don't need to do it manually, and potentially forget.
For example, this allows to do:

  my_flags flags;

  ...

  flags |= some_flag;

gdb/ChangeLog:

	* common/enum-flags.h (enum_flags::enum_flags): Initialize
	m_enum_value to 0 in default constructor.