Makefile: Mark unsupported libraries for DOS (DJGPP)

DOS will probably never get USB support.

Change-Id: I6bcc67dc35740b58752663bfcb1c947ba7f70581
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/73771
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Makefile b/Makefile
index 39a4b72..bf02618 100644
--- a/Makefile
+++ b/Makefile
@@ -274,6 +274,9 @@
 endif
 
 ifeq ($(TARGET_OS), DOS)
+$(call mark_unsupported,$(DEPENDS_ON_LIBFTDI1))
+$(call mark_unsupported,$(DEPENDS_ON_LIBUSB1))
+$(call mark_unsupported,CONFIG_JLINK_SPI)
 # DJGPP has odd uint*_t definitions which cause lots of format string warnings.
 override CFLAGS += -Wno-format
 override LDFLAGS += -lgetopt