selftests/bpf: Fix wrong binary in Makefile log output

selftests/bpf: Fix wrong binary in Makefile log output

Make log output incorrectly shows 'test_maps' as the binary name for every
'CLNG-BPF' build step, apparently picking up the last value defined for the
$(TRUNNER_BINARY) variable. Update the 'CLANG_BPF_BUILD_RULE' variants to
fix this confusing output.

Current output:
  CLNG-BPF [test_maps] access_map_in_map.bpf.o
  GEN-SKEL [test_progs] access_map_in_map.skel.h
  ...
  CLNG-BPF [test_maps] access_map_in_map.bpf.o
  GEN-SKEL [test_progs-no_alu32] access_map_in_map.skel.h
  ...
  CLNG-BPF [test_maps] access_map_in_map.bpf.o
  GEN-SKEL [test_progs-cpuv4] access_map_in_map.skel.h

After fix:
  CLNG-BPF [test_progs] access_map_in_map.bpf.o
  GEN-SKEL [test_progs] access_map_in_map.skel.h
  ...
  CLNG-BPF [test_progs-no_alu32] access_map_in_map.bpf.o
  GEN-SKEL [test_progs-no_alu32] access_map_in_map.skel.h
  ...
  CLNG-BPF [test_progs-cpuv4] access_map_in_map.bpf.o
  GEN-SKEL [test_progs-cpuv4] access_map_in_map.skel.h

Fixes: a5d0c26a2784 ("selftests/bpf: Add a cpuv4 test runner for cpu=v4 testing")
Fixes: 89ad7420b25c ("selftests/bpf: Drop the need for LLVM's llc")
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240720052535.2185967-1-tony.ambardar@gmail.com