selftests/bpf: Fix runqslower cross-endian build

The runqslower binary from a cross-endian build currently fails to run
because the included skeleton has host endianness. Fix this by passing the
target BPF endianness to the runqslower sub-make.

Fixes: 5a63c33d6f ("selftests/bpf: Support cross-endian building")
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250125071423.2603588-1-itugrok@yahoo.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/runqslower/Makefile

@@ -6,6 +6,7 @@ OUTPUT ?= $(abspath .output)/
 BPFTOOL_OUTPUT := $(OUTPUT)bpftool/
 DEFAULT_BPFTOOL := $(BPFTOOL_OUTPUT)bootstrap/bpftool
 BPFTOOL ?= $(DEFAULT_BPFTOOL)
+BPF_TARGET_ENDIAN ?= --target=bpf
 LIBBPF_SRC := $(abspath ../../lib/bpf)
 BPFOBJ_OUTPUT := $(OUTPUT)libbpf/
 BPFOBJ := $(BPFOBJ_OUTPUT)libbpf.a
@@ -63,7 +64,7 @@ $(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o | $(BPFTOOL)
 	$(QUIET_GEN)$(BPFTOOL) gen skeleton $< > $@
 
 $(OUTPUT)/%.bpf.o: %.bpf.c $(BPFOBJ) | $(OUTPUT)
-	$(QUIET_GEN)$(CLANG) -g -O2 --target=bpf $(INCLUDES)		      \
+	$(QUIET_GEN)$(CLANG) -g -O2 $(BPF_TARGET_ENDIAN) $(INCLUDES)	      \
 		 -c $(filter %.c,$^) -o $@ &&				      \
 	$(LLVM_STRIP) -g $@
 

tools/testing/selftests/bpf/Makefile

@@ -306,6 +306,7 @@ $(OUTPUT)/runqslower: $(BPFOBJ) | $(DEFAULT_BPFTOOL) $(RUNQSLOWER_OUTPUT)
 		    BPFTOOL_OUTPUT=$(HOST_BUILD_DIR)/bpftool/		       \
 		    BPFOBJ_OUTPUT=$(BUILD_DIR)/libbpf/			       \
 		    BPFOBJ=$(BPFOBJ) BPF_INCLUDE=$(INCLUDE_DIR)		       \
+		    BPF_TARGET_ENDIAN=$(BPF_TARGET_ENDIAN)		       \
 		    EXTRA_CFLAGS='-g $(OPT_FLAGS) $(SAN_CFLAGS) $(EXTRA_CFLAGS)' \
 		    EXTRA_LDFLAGS='$(SAN_LDFLAGS) $(EXTRA_LDFLAGS)' &&	       \
 		    cp $(RUNQSLOWER_OUTPUT)runqslower $@