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.

scripts/mysql_config.sh

@@ -87,6 +87,8 @@ pkglibdir='@pkglibdir@'
 pkglibdir_rel=`echo $pkglibdir | sed -e "s;^$basedir/;;"`
 fix_path pkglibdir $pkglibdir_rel lib/mysql lib
 
+plugindir='@pkgplugindir@'
+
 pkgincludedir='@pkgincludedir@'
 fix_path pkgincludedir include/mysql include
 
@@ -147,6 +149,7 @@ Options:
         --include        [$include]
         --libs           [$libs]
         --libs_r         [$libs_r]
+        --plugindir      [$plugindir]
         --socket         [$socket]
         --port           [$port]
         --version        [$version]
@@ -163,6 +166,7 @@ while test $# -gt 0; do
         --include) echo "$include" ;;
         --libs)    echo "$libs" ;;
         --libs_r)  echo "$libs_r" ;;
+        --plugindir) echo "$plugindir" ;;
         --socket)  echo "$socket" ;;
         --port)    echo "$port" ;;
         --version) echo "$version" ;;