cmake: Install libraries according to multi-arch rules

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

CMakeLists.txt

@@ -22,6 +22,7 @@ set( TQT_VERSION "${TQT_MAJOR_VERSION}.${TQT_MINOR_VERSION}.${TQT_MICRO_VERSION}
 cmake_minimum_required( VERSION 2.8 )
 
 include( CheckCXXSourceCompiles )
+include( GNUInstallDirs OPTIONAL )
 
 
 ##### include our cmake modules #################
@@ -34,7 +35,11 @@ include( TDEMacros )
 
 tde_setup_install_path( EXEC_INSTALL_PREFIX   "${CMAKE_INSTALL_PREFIX}" )
 tde_setup_install_path( BIN_INSTALL_DIR       "${EXEC_INSTALL_PREFIX}/bin"  )
-tde_setup_install_path( LIB_INSTALL_DIR       "${EXEC_INSTALL_PREFIX}/lib${LIB_SUFFIX}" )
+if( CMAKE_INSTALL_LIBDIR )
+  tde_setup_install_path( LIB_INSTALL_DIR     "${EXEC_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}" )
+else( )
+  tde_setup_install_path( LIB_INSTALL_DIR     "${EXEC_INSTALL_PREFIX}/lib${LIB_SUFFIX}" )
+endif( )
 tde_setup_install_path( INCLUDE_INSTALL_DIR   "${CMAKE_INSTALL_PREFIX}/include/tqt" )
 tde_setup_install_path( PKGCONFIG_INSTALL_DIR "${LIB_INSTALL_DIR}/pkgconfig" )