Backport from trunk:

Bug #18382225 MYSQL_CONFIG CAN'T HANDLE RELOCABLE PACKAGES THAT USES "LIB64" OR "-64" SUFFIX
  
'lib' is hardcoded into mysql_config, so 'cmake -DINSTALL_LIBDIR=lib64' will not work.
Use INSTALL_LIBDIR when generating mysql_config.
  
mysql_config may be renamed to e.g. mysql_config-32, fix the basedir pattern matching.

scripts/CMakeLists.txt

@@ -223,6 +223,7 @@ SET(libexecdir ${prefix}/${INSTALL_SBINDIR})
 SET(scriptdir ${prefix}/${INSTALL_BINDIR})
 SET(datadir ${prefix}/${INSTALL_MYSQLSHAREDIR})
 SET(pkgdatadir ${prefix}/${INSTALL_MYSQLSHAREDIR})
+SET(libsubdir  ${INSTALL_LIBDIR})
 SET(pkgincludedir ${prefix}/${INSTALL_INCLUDEDIR})
 SET(pkglibdir ${prefix}/${INSTALL_LIBDIR})
 SET(pkgplugindir ${prefix}/${INSTALL_PLUGINDIR})

scripts/mysql_config.sh

@@ -76,7 +76,8 @@ get_full_path ()
 
 me=`get_full_path $0`
 
-basedir=`echo $me | sed -e 's;/bin/mysql_config;;'`
+# Script might have been renamed but assume mysql_<something>config<something>
+basedir=`echo $me | sed -e 's;/bin/mysql_.*config.*;;'`
 
 ldata='@localstatedir@'
 execdir='@libexecdir@'
@@ -85,11 +86,11 @@ bindir='@bindir@'
 # If installed, search for the compiled in directory first (might be "lib64")
 pkglibdir='@pkglibdir@'
 pkglibdir_rel=`echo $pkglibdir | sed -e "s;^$basedir/;;"`
-fix_path pkglibdir $pkglibdir_rel lib/mysql lib
+fix_path pkglibdir $pkglibdir_rel @libsubdir@/mysql @libsubdir@
 
 plugindir='@pkgplugindir@'
 plugindir_rel=`echo $plugindir | sed -e "s;^$basedir/;;"`
-fix_path plugindir $plugindir_rel lib/mysql/plugin lib/plugin
+fix_path plugindir $plugindir_rel @libsubdir@/mysql/plugin @libsubdir@/plugin
 
 pkgincludedir='@pkgincludedir@'
 if [ -f "$basedir/include/mysql/mysql.h" ]; then