Rename feature variable clang-bpf-global-var following upstream changes. This restores the HAVE_CLANG feature override and should avoid rare build errors where a recent host clang and BTF-enabled host kernel are present. Fixes:23be333401("bpftools: update to 5.10.10") Signed-off-by: Tony Ambardar <itugrok@yahoo.com> (cherry picked from commitcf20f1bb5f)