Bug #11759877 52223: TEST "PLUGIN_DIR_BASIC" DOES NOT SUPPORT RPM BUILD (TEST) DIRECTORY STRUC

Make a qualified guess: if $basedir/lib does not exist but $basedir/lib64
  does, then the latter is the proper value for $MYSQL_LIBDIR
Tested on the RPMS of 5.5.12.

mysql-test/mysql-test-run.pl

@@ -2220,7 +2220,12 @@ sub environment_setup {
   $ENV{'DEFAULT_MASTER_PORT'}= $mysqld_variables{'port'};
   $ENV{'MYSQL_TMP_DIR'}=      $opt_tmpdir;
   $ENV{'MYSQLTEST_VARDIR'}=   $opt_vardir;
+  # Used for guessing default plugin dir, we can't really know for sure
   $ENV{'MYSQL_LIBDIR'}=       "$basedir/lib";
+  # Override if this does not exist, but lib64 does (best effort)
+  if (! -d "$basedir/lib" && -d "$basedir/lib64") {
+    $ENV{'MYSQL_LIBDIR'}=     "$basedir/lib64";
+  }
   $ENV{'MYSQL_BINDIR'}=       "$bindir";
   $ENV{'MYSQL_SHAREDIR'}=     $path_language;
   $ENV{'MYSQL_CHARSETSDIR'}=  $path_charsetsdir;