package/libbpf: add BR2_PACKAGE_LIBBPF_ARCH_SUPPORTS

libbpf does not support all architectures, for example ARM is not
supported resulting in the following build failure:

bpf.c:53:4: 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/288d54100a2e736195a3a04a9e2e035d02ea5c16

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/libbpf/Config.in

@@ -1,5 +1,15 @@
+config BR2_PACKAGE_LIBBPF_ARCH_SUPPORTS
+	bool
+	# see 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_LIBBPF
 	bool "libbpf"
+	depends on BR2_PACKAGE_LIBBPF_ARCH_SUPPORTS
 	depends on BR2_USE_WCHAR # elfutils
 	depends on !BR2_STATIC_LIBS # elfutils
 	depends on BR2_TOOLCHAIN_HAS_THREADS # elfutils
@@ -15,6 +25,7 @@ config BR2_PACKAGE_LIBBPF
 	  https://github.com/libbpf/libbpf
 
 comment "libbpf needs a uClibc or glibc toolchain w/ wchar, dynamic library, threads"
+	depends on BR2_PACKAGE_LIBBPF_ARCH_SUPPORTS
 	depends on !BR2_USE_WCHAR || BR2_STATIC_LIBS \
 		|| !BR2_TOOLCHAIN_HAS_THREADS \
 		|| !(BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC)