btf: require pahole 1.21+ for DEBUG_INFO_BTF with default DWARF version

btf: require pahole 1.21+ for DEBUG_INFO_BTF with default DWARF version

As described in commit 42d9b379e3e1 ("lib/Kconfig.debug: Allow BTF +
DWARF5 with pahole 1.21+"), the combination of CONFIG_DEBUG_INFO_BTF
and CONFIG_DEBUG_INFO_DWARF5 requires pahole 1.21+.

GCC 11+ and Clang 14+ default to DWARF 5 when the -g flag is passed.
For the same reason, the combination of CONFIG_DEBUG_INFO_BTF and
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is also likely to require
pahole 1.21+ these days. (At least, it is uncertain whether the actual
requirement is pahole 1.16+ or 1.21+.)

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240913173759.1316390-3-masahiroy@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>