kernel-open: fix BTF generation on kernel 6.15+

Kernel 6.15+ replaced scripts/pahole-flags.sh with scripts/Makefile.btf
and scripts/gen-btf.sh for BTF generation. The existing check only looks
for pahole-flags.sh, causing the PAHOLE_AWK_PROGRAM wrapper to be used
unnecessarily on newer kernels. This wrapper has shell quoting issues
that result in awk parse errors during module build.

Update the condition to also check for Makefile.btf, allowing the kernel's
native BTF infrastructure to handle generation without the awk wrapper.

Signed-off-by: Cole Leavitt <cole@unwrap.rs>

Author: coleleavitt

kernel-open/Makefile

@@ -92,10 +92,11 @@ else
   #     system(pahole_cmd)
   # }
   PAHOLE_AWK_PROGRAM = BEGIN { pahole_cmd = \"pahole\"; for (i = 1; i < ARGC; i++) { if (ARGV[i] ~ /--lang_exclude=/) { pahole_cmd = pahole_cmd sprintf(\" %s,c++\", ARGV[i]); } else { pahole_cmd = pahole_cmd sprintf(\" %s\", ARGV[i]); } } system(pahole_cmd); }
-  # If scripts/pahole-flags.sh is not present in the kernel tree, add PAHOLE and
-  # PAHOLE_AWK_PROGRAM assignments to PAHOLE_VARIABLES; otherwise assign the
-  # empty string to PAHOLE_VARIABLES.
-  PAHOLE_VARIABLES=$(if $(wildcard $(KERNEL_SOURCES)/scripts/pahole-flags.sh),,"PAHOLE=$(AWK) '$(PAHOLE_AWK_PROGRAM)'")
+  # If scripts/pahole-flags.sh or scripts/Makefile.btf is present in the kernel
+  # tree, the kernel handles BTF generation natively; otherwise add PAHOLE and
+  # PAHOLE_AWK_PROGRAM assignments to PAHOLE_VARIABLES.
+  # Kernel 6.15+ uses Makefile.btf + gen-btf.sh instead of pahole-flags.sh.
+  PAHOLE_VARIABLES=$(if $(or $(wildcard $(KERNEL_SOURCES)/scripts/pahole-flags.sh),$(wildcard $(KERNEL_SOURCES)/scripts/Makefile.btf)),,"PAHOLE=$(AWK) '$(PAHOLE_AWK_PROGRAM)'")
 
   ifndef ARCH
     ARCH := $(shell uname -m | sed -e 's/i.86/i386/' \