Makefile: Mark Linux-specific libgpiod as unsupported on other OS's

Change-Id: Ia453149bd0883900d470303337e772b8f7f716fa
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/73772
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Makefile b/Makefile
index bf02618..7bd4de9 100644
--- a/Makefile
+++ b/Makefile
@@ -333,6 +333,11 @@
 $(call mark_unsupported,$(DEPENDS_ON_LINUX_I2C))
 endif
 
+# libgpiod is most likely not available on anything but Linux and Android
+ifeq ($(filter $(TARGET_OS), Linux Android), )
+$(call mark_unsupported,$(DEPENDS_ON_LIBGPIOD))
+endif
+
 ifeq ($(TARGET_OS), Android)
 # Android on x86 (currently) does not provide raw PCI port I/O operations.
 $(call mark_unsupported,$(DEPENDS_ON_X86_PORT_IO))