kbuild,bpf: Switch to using --btf_features for pahole v1.26 and later

The btf_features list can be used for pahole v1.26 and later -
it is useful because if a feature is not yet implemented it will
not exit with a failure message.  This will allow us to add feature
requests to the pahole options without having to check pahole versions
in future; if the version of pahole supports the feature it will be
added.
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240507135514.490467-1-alan.maguire@oracle.com

scripts/Makefile.btf

@@ -3,6 +3,8 @@
 pahole-ver := $(CONFIG_PAHOLE_VERSION)
 pahole-flags-y :=
 
+ifeq ($(call test-le, $(pahole-ver), 125),y)
+
 # pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
 ifeq ($(call test-le, $(pahole-ver), 121),y)
 pahole-flags-$(call test-ge, $(pahole-ver), 118)	+= --skip_encoding_btf_vars
@@ -12,8 +14,17 @@ pahole-flags-$(call test-ge, $(pahole-ver), 121)	+= --btf_gen_floats
 
 pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j
 
-pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
+ifeq ($(pahole-ver), 125)
+pahole-flags-y	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
+endif
+
+else
 
-pahole-flags-$(call test-ge, $(pahole-ver), 125)	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
+# Switch to using --btf_features for v1.26 and later.
+pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
+
+endif
+
+pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
 
 export PAHOLE_FLAGS := $(pahole-flags-y)