This reverts commit b9ace36fcc.
This change was added by PR 625 but has a serious logic flaw. It removes all occurrences of INCDIROPT and replaces it with a definition in tools/Config.mk:
else ifeq ($(WINTOOL),y)
DEFINE = "$(TOPDIR)/tools/define.sh"
INCDIR = "$(TOPDIR)/tools/incdir.sh" -w
This logic flaw is the Config.mk is included in all Make.defs files BEFORE WINTOOL is defined. As a result, the definition is wrong in many places when building under Cygwin with a Windows native toolchain.
