bug#51925: 5.5 installed header file layout is incorrect

The 'mysql' include sub-directory was copied directly into
include/ rather than retaining its own directory.

Fix this, and update mysql_config which needs additional
logic to detect the correct prefix for includes.

include/CMakeLists.txt

@@ -59,6 +59,4 @@ SET(HEADERS
 )
 
 INSTALL(FILES ${HEADERS} DESTINATION ${INSTALL_INCLUDEDIR} COMPONENT Development)
-INSTALL(DIRECTORY mysql/ DESTINATION ${INSTALL_INCLUDEDIR}  COMPONENT Development FILES_MATCHING PATTERN "*.h" )
-
-
+INSTALL(DIRECTORY mysql/ DESTINATION ${INSTALL_INCLUDEDIR}/mysql COMPONENT Development FILES_MATCHING PATTERN "*.h")

scripts/mysql_config.sh

@@ -92,7 +92,11 @@ plugindir_rel=`echo $plugindir | sed -e "s;^$basedir/;;"`
 fix_path plugindir $plugindir_rel lib/mysql/plugin lib/plugin
 
 pkgincludedir='@pkgincludedir@'
-fix_path pkgincludedir include/mysql include
+if [ -f $basedir/include/mysql/mysql.h ]; then
+  pkgincludedir="$basedir/include/mysql"
+elif [ -f $basedir/include/mysql.h ]; then
+  pkgincludedir="$basedir/include"
+fi
 
 version='@VERSION@'
 socket='@MYSQL_UNIX_ADDR@'