samples: uhid: build sample program for target architecture

This userspace program includes UAPI headers exported to usr/include/.
'make headers' always works for the target architecture (i.e. the same
architecture as the kernel), so the sample program should be built for
the target as well. Kbuild now supports 'userprogs' for that.

Add the entry to samples/Makefile to put this into the build bot
coverage.

I also added the CONFIG option guarded by 'depends on CC_CAN_LINK'
because $(CC) may not provide libc.

Signed-off-by: Masahiro Yamada <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>

samples/Kconfig

···
 	  Build samples of seccomp filters using various methods of
 	  BPF filter construction.
 
+config SAMPLE_UHID
+	bool "UHID sample"
+	depends on CC_CAN_LINK && HEADERS_INSTALL
+	help
+	  Build UHID sample program.
+
 config SAMPLE_VFIO_MDEV_MTTY
 	tristate "Build VFIO mtty example mediated device sample code -- loadable modules only"
 	depends on VFIO_MDEV_DEVICE && m

samples/Makefile

···
 obj-$(CONFIG_SAMPLE_TRACE_PRINTK)	+= trace_printk/
 obj-$(CONFIG_SAMPLE_FTRACE_DIRECT)	+= ftrace/
 obj-$(CONFIG_SAMPLE_TRACE_ARRAY)	+= ftrace/
+subdir-$(CONFIG_SAMPLE_UHID)		+= uhid
 obj-$(CONFIG_VIDEO_PCI_SKELETON)	+= v4l/
 obj-y					+= vfio-mdev/
 subdir-$(CONFIG_SAMPLE_VFS)		+= vfs

samples/uhid/.gitignore

···
+# SPDX-License-Identifier: GPL-2.0-only
+/uhid-example

samples/uhid/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-# List of programs to build
-hostprogs := uhid-example
+userprogs := uhid-example
+always-y := $(userprogs)
 
-# Tell kbuild to always build the programs
-always-y := $(hostprogs)
-
-HOSTCFLAGS_uhid-example.o += -I$(objtree)/usr/include
+userccflags += -I usr/include