fix build of bundled python3 with bundled zlib

Change-Id: I383a04ea926187263b1d7e11c548817fa9ca3fb6

external/python3/ExternalProject_python3.mk

@@ -99,6 +99,7 @@ $(call gb_ExternalProject_get_state_target,python3,build) :
 			)" \
 		&& MAKEFLAGS= $(MAKE) \
 			$(if $(filter MACOSX,$(OS)),DESTDIR=$(EXTERNAL_WORKDIR)/python-inst install) \
+			$(if $(SYSTEM_ZLIB),,ZLIB_INCDIR=$(WORKDIR)/UnpackedTarball/zlib) \
 		&& ln -s build/lib.* LO_lib \
 	)
 

external/python3/internal-zlib.patch.0

@@ -19,6 +19,15 @@
  
 --- setup.py
 +++ setup.py
+@@ -1362,7 +1362,7 @@
+         #
+         # You can upgrade zlib to version 1.1.4 yourself by going to
+         # http://www.gzip.org/zlib/
+-        zlib_inc = find_file('zlib.h', [], inc_dirs)
++        zlib_inc = [os.environ.get('ZLIB_INCDIR')]
+         have_zlib = False
+         if zlib_inc is not None:
+             zlib_h = zlib_inc[0] + '/zlib.h'
 @@ -1379,13 +1379,13 @@
                          version = line.split()[2]
                          break