build: Replace WINTOOL with CYGWIN_WINTOOL Kconfig

so the correct value can be determinated by Kconfig system automatically

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

boards/arm/stm32/fire-stm32v2/scripts/Make.defs

@@ -45,7 +45,7 @@ else
   LDSCRIPT = fire-stm32v2.ld
 endif
 
-ifeq ($(WINTOOL),y)
+ifeq ($(CONFIG_CYGWIN_WINTOOL),y)
   # Windows-native toolchains
   DIRLINK = $(TOPDIR)/tools/copydir.sh
   DIRUNLINK = $(TOPDIR)/tools/unlink.sh