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: 23be333401f0 ("bpftools: update to 5.10.10")
Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
Signed-off-by: maurerr <mariusd84@gmail.com>