SuperBuild: fix lib64 install dir on CentOS

SuperBuild/patches/GDAL/gdal-6-pythonInstall-all.diff

 --- gdal-2.2.1-orig/swig/python/GNUmakefile	2017-06-23 14:18:44.000000000 +0200
-+++ gdal-2.2.1/swig/python/GNUmakefile	2018-03-09 18:44:06.533081541 +0100
++++ gdal-2.2.1/swig/python/GNUmakefile	2018-03-13 17:20:34.951592209 +0100
 @@ -81,18 +81,7 @@
  endif
  
@@ -7,7 +7,7 @@
 -    ifeq ($(shell uname),Darwin)
 -        STD_UNIX_LAYOUT=$(shell $(PYTHON) -c "from __future__ import print_function;import sys;print(\"FALSE\" if \"framework\" in sys.prefix.lower() else \"TRUE\")")
 -        ifeq ($(STD_UNIX_LAYOUT),"TRUE")
-             setup_opts+=--prefix=$(prefix)
+-            setup_opts+=--prefix=$(prefix)
 -        else
 -            ifdef PYTHON_INSTALL_LIB
 -                setup_opts+=--install-lib=$(PYTHON_INSTALL_LIB)
@@ -16,6 +16,7 @@
 -    else
 -        setup_opts+=--prefix=$(prefix)
 -    endif
++    setup_opts+=--install-lib=$(site_package_dir)
  endif
  
  ifdef INSTALL_LAYOUT