samples: seccomp: build sample programs for target architecture

These userspace programs include 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 programs should be built for
the target as well. Kbuild now supports 'userprogs' for that.

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

The 'ifndef CROSS_COMPILE' is no longer needed.

BTW, the -m31 for s390 is left-over code. Commit 5a79859a ("s390:
remove 31 bit support") killed it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

samples/Kconfig

@@ -126,7 +126,7 @@ config SAMPLE_PIDFD
 
 config SAMPLE_SECCOMP
 	bool "Build seccomp sample code"
-	depends on SECCOMP_FILTER && HEADERS_INSTALL
+	depends on SECCOMP_FILTER && CC_CAN_LINK && HEADERS_INSTALL
 	help
 	  Build samples of seccomp filters using various methods of
 	  BPF filter construction.

samples/seccomp/Makefile

 # SPDX-License-Identifier: GPL-2.0
-ifndef CROSS_COMPILE
-hostprogs := bpf-fancy dropper bpf-direct user-trap
+userprogs := bpf-fancy dropper bpf-direct user-trap
 
-HOSTCFLAGS_bpf-fancy.o += -I$(objtree)/usr/include
-HOSTCFLAGS_bpf-fancy.o += -idirafter $(objtree)/include
-HOSTCFLAGS_bpf-helper.o += -I$(objtree)/usr/include
-HOSTCFLAGS_bpf-helper.o += -idirafter $(objtree)/include
 bpf-fancy-objs := bpf-fancy.o bpf-helper.o
 
-HOSTCFLAGS_dropper.o += -I$(objtree)/usr/include
-HOSTCFLAGS_dropper.o += -idirafter $(objtree)/include
-dropper-objs := dropper.o
+userccflags += -I usr/include
 
-HOSTCFLAGS_bpf-direct.o += -I$(objtree)/usr/include
-HOSTCFLAGS_bpf-direct.o += -idirafter $(objtree)/include
-bpf-direct-objs := bpf-direct.o
-
-HOSTCFLAGS_user-trap.o += -I$(objtree)/usr/include
-HOSTCFLAGS_user-trap.o += -idirafter $(objtree)/include
-user-trap-objs := user-trap.o
-
-# Try to match the kernel target.
-ifndef CONFIG_64BIT
-
-# s390 has -m31 flag to build 31 bit binaries
-ifndef CONFIG_S390
-MFLAG = -m32
-else
-MFLAG = -m31
-endif
-
-HOSTCFLAGS_bpf-direct.o += $(MFLAG)
-HOSTCFLAGS_dropper.o += $(MFLAG)
-HOSTCFLAGS_bpf-helper.o += $(MFLAG)
-HOSTCFLAGS_bpf-fancy.o += $(MFLAG)
-HOSTCFLAGS_user-trap.o += $(MFLAG)
-HOSTLDLIBS_bpf-direct += $(MFLAG)
-HOSTLDLIBS_bpf-fancy += $(MFLAG)
-HOSTLDLIBS_dropper += $(MFLAG)
-HOSTLDLIBS_user-trap += $(MFLAG)
-endif
-always-y := $(hostprogs)
-endif
+always-y := $(userprogs)