This fixes tons of warnings with clang from a recent xcode version on
macOS (and possibly other systems) complaining that an instantiation
of _singleton is required but no definition is available.
Silences the clang warning:
static data member specialization of '_singleton' must
originally be declared in namespace 'Common'; accepted as a C++0x
extension [-Wc++0x-extensions]
Wrapping "namespace Common {}" around the macro assignment causes clang
to complain about a spurious semicolon, and removing the semicolon at
the end of the macro causes some editors to misbehave.
Changing the requirement of using the macro in one namespace (the
global) to another (Common) seems a small price to pay to
silence a warning.
This makes it possible to write
DECLARE_SINGLETON(foo);
instead of
DECLARE_SINGLETON(foo)
without causing a warning about an extra semicolon.
The extra semicolon helps some editors at parsing the C++ code.
svn-id: r54258
