With global NLS support enabled (CONFIG_BUILD_NLS), the linked libelf.so
and libbfd.so libraries will depend on libintl.so. Import the nls.mk helper
to set library prefixes and flags accordingly, and also conditionally add
"-lintl" as link-time library.

Fix a build error on ppc due to a EDEADLOCK redefinition in errno.h.

Use upstream stable kernel 5.8.9, and fix overriding of feature detection
to only allow/hide detected features. Also refresh existing patches.

Fixes: 2f0d6720 ("bpftools: add utility and library packages supporting
eBPF usage")

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>