selftests/bpf: fix Makefile for passing LLC to the command line

Makefile has a LLC variable that is initialised to "llc", but can
theoretically be overridden from the command line ("make LLC=llc-6.0").
However, this fails because for LLVM probe check, "llc" is called
directly. Use the $(LLC) variable instead to fix this.

Fixes: 22c8852624 ("bpf: improve selftests and add tests for meta pointer")
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/Makefile

@@ -39,7 +39,7 @@ $(BPFOBJ): force
 CLANG ?= clang
 LLC   ?= llc
 
-PROBE := $(shell llc -march=bpf -mcpu=probe -filetype=null /dev/null 2>&1)
+PROBE := $(shell $(LLC) -march=bpf -mcpu=probe -filetype=null /dev/null 2>&1)
 
 # Let newer LLVM versions transparently probe the kernel for availability
 # of full BPF instruction set.