Add new pkgplugindir handling to seperate plugins from libraries,

and allow override for binary distributions.  Extend mysql_config
to print compiled-in plugin location for third-party plugins to
use.  Resolves bug#31736.


libmysqld/Makefile.am:
  Use pkgplugindir.
plugin/daemon_example/Makefile.am:
  Use pkgplugindir.
plugin/fulltext/Makefile.am:
  Use pkgplugindir.
scripts/Makefile.am:
  Add pkgplugindir.
scripts/make_binary_distribution.sh:
  Add pkgplugindir.
scripts/mysql_config.sh:
  Add pkgplugindir.
sql/Makefile.am:
  Use pkgplugindir.
sql/mysqld.cc:
  Use PLUGINDIR, derived from pkgplugindir, instead of
  LIBDIR for plugins.
sql/unireg.h:
  Use PLUGINDIR instead of LIBDIR, and define to be the
  default setting of pkgplugindir.
storage/innobase/Makefile.am:
  Use pkgplugindir.
storage/archive/Makefile.am:
  Use pkgplugindir.
storage/blackhole/Makefile.am:
  Use pkgplugindir.
storage/example/Makefile.am:
  Use pkgplugindir.
storage/federated/Makefile.am:
  Use pkgplugindir.

storage/blackhole/Makefile.am

@@ -19,6 +19,7 @@ MYSQLDATAdir =          $(localstatedir)
 MYSQLSHAREdir =         $(pkgdatadir)
 MYSQLBASEdir=           $(prefix)
 MYSQLLIBdir=            $(pkglibdir)
+pkgplugindir =		$(libdir)/@PACKAGE@/plugin
 INCLUDES =              -I$(top_srcdir)/include -I$(top_builddir)/include \
 			-I$(top_srcdir)/regex \
 			-I$(top_srcdir)/sql \
@@ -32,8 +33,8 @@ DEFS =                  @DEFS@
 noinst_HEADERS =	ha_blackhole.h
 
 EXTRA_LTLIBRARIES =	ha_blackhole.la
-pkglib_LTLIBRARIES =	@plugin_blackhole_shared_target@
-ha_blackhole_la_LDFLAGS=-module -rpath $(MYSQLLIBdir)
+pkgplugin_LTLIBRARIES =	@plugin_blackhole_shared_target@
+ha_blackhole_la_LDFLAGS=-module -rpath $(pkgplugindir)
 ha_blackhole_la_CXXFLAGS=$(AM_CFLAGS) -DMYSQL_DYNAMIC_PLUGIN
 ha_blackhole_la_CFLAGS=	$(AM_CFLAGS) -DMYSQL_DYNAMIC_PLUGIN
 ha_blackhole_la_SOURCES=ha_blackhole.cc