core: config: Use host bison if requested

# To run bison from elsewhere you need to set up enviromental variable

# BISON_PKGDATADIR.

BISON_PKGDATADIR := $(PWD)/external/bison/data

ifeq ($(USE_HOST_BISON),yes)

BISON := bison

else

BISON := prebuilts/misc/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/bison/bison

endif

YACC := $(BISON) -d

YASM := prebuilts/misc/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/yasm/yasm