package/bpftool: add BR2_PACKAGE_BPFTOOL_ARCH_SUPPORTS

bpftool uses its own local copy of libbpf so add
BR2_PACKAGE_BPFTOOL_ARCH_SUPPORTS to avoid the following build failure
on ARM:

btf.c: In function 'btf_type_by_id':
btf.c:461:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (type_id < btf->start_id)
              ^
bpf.c:62:4: error: #error __NR_bpf not defined. libbpf does not support your arch.
 #  error __NR_bpf not defined. libbpf does not support your arch.
    ^

Fixes:
 - http://autobuild.buildroot.org/results/aae772f1cfb16516a57f310c4f022e80a2a8d65e

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit c750dd4e5d03430148841d2d897e90dbe19ce172)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/bpftool/Config.in

@@ -1,5 +1,15 @@
+config BR2_PACKAGE_BPFTOOL_ARCH_SUPPORTS
+	bool
+	# see libbpf/src/bpf.c
+	default y if BR2_arc
+	default y if BR2_aarch64 || BR2_aarch64_be
+	default y if BR2_i386 || BR2_x86_64
+	default y if BR2_sparc || BR2_sparc64
+	default y if BR2_s390x
+
 config BR2_PACKAGE_BPFTOOL
 	bool "bpftool"
+	depends on BR2_PACKAGE_BPFTOOL_ARCH_SUPPORTS
 	depends on !BR2_nios2 # binutils
 	depends on BR2_USE_WCHAR # binutils, elfutils
 	depends on !BR2_STATIC_LIBS # elfutils
@@ -13,6 +23,7 @@ config BR2_PACKAGE_BPFTOOL
 	  of eBPF programs and maps.
 
 comment "bpftool needs a uClibc or glibc toolchain w/ wchar, dynamic library, threads, headers >= 4.12"
+	depends on BR2_PACKAGE_BPFTOOL_ARCH_SUPPORTS
 	depends on !BR2_nios2
 	depends on !BR2_USE_WCHAR || BR2_STATIC_LIBS \
 		|| !BR2_TOOLCHAIN_HAS_THREADS \