gbuild: More crude hacking to fix over-evaluation of gb_Python_PRECOMMAND
gbuild: More crude hacking to fix over-evaluation of gb_Python_PRECOMMAND

...in the spirit of 3e70e26cbc96667e2968cd325737053bf8bffb78 "gbuild: fix over-
evaluation in gb_ExternalExecutable__set_internal"

Change-Id: I3d5859bd3437cc050250e66d723d3dee3056ef46

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core