Fixed main.mysql_upgrade to pass when unix_socket plugin is unavailable.
Also don't redefine _GNU_SOURCE, which was previously defined by command
line/environment. This fixes silent auth_socket build failure with
MYSQL_MAINTAINER_MODE=ERR.
Remove ONLY_IF clause in MYSQL_ADD_PLUGIN and the requirement
that every plugin's CMakeLists.txt *must* do MYSQL_ADD_PLUGIN
for PLUGIN_XXX=YES to work. This was very fragile and cannot be
relied on.
Use a different implementation of =YES check - iterate all
PLUGIN_* variables and see which one doesn't have a matching target.
Revert all ONLY_IF changes in CMakeLists.txt files.
* Introduce a set of PLUGIN_xxx cmake options with values
NO, STATIC, DYNAMIC, AUTO, YES (abort if plugin is not compiled)
* Deprecate redundant and ambiguous WITH_xxx, WITH_PLUGIN_xxx,
WITH_xxx_STORAGE_ENGINE, WITHOUT_xxx, WITHOUT_PLUGIN_xxx,
WITHOUT_xxx_STORAGE_ENGINE
* Actually check whether a plugin is disabled (DISABLED keyword was
always present, but it was ignored until now).
* Support conditionally disabled plugins - keyword ONLY_IF
* Use ONLY_IF for conditionally skipping plugins, instead of
doing MYSQL_ADD_PLUGIN conditionally as before. Because if
MYSQL_ADD_PLUGIN isn't done at all, PLUGIN_xxx=YES cannot work.
out of libmysql into separate dynamic plugins in the plugin/ directory.
move dialog and auth_socket plugins out of the plugin directory with examples into
dedicated directories in plugin/
