devel/binutils: Enable shared

The submittor's reason for this change is that shared libraries makes
dependencies easier to track. However, this is not the primary reason
to add shared library support. Shared libraries are more secure because
should a depending package, such as binutils, require a security update
any depending packages will immediately reap the benefit of the newly
secured package.

This change only affects the native flavor because when 2f26d37a5937
(SVN r517642) changed the port from slave ports of binutils to FLAVORS,
it mistakenly removed shared libraries from the native package. Prior to
this 2f26d37a5937 only non-native packages were built producing only
static libraries. This revision restores the behabviour of prior to
2f26d37a5937.

PR: 270146
Reported by: yuri
Fixes: 2f26d37a5937 (SVN r517642)