selftests/bpf: Forward SAN_CFLAGS and SAN_LDFLAGS to runqslower and libbpf

To get useful results from the Memory Sanitizer, all code running in a
process needs to be instrumented. When building tests with other
sanitizers, it's not strictly necessary, but is also helpful.
So make sure runqslower and libbpf are compiled with SAN_CFLAGS and
linked with SAN_LDFLAGS.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230210001210.395194-5-iii@linux.ibm.com

tools/testing/selftests/bpf/Makefile

@@ -215,7 +215,9 @@ $(OUTPUT)/runqslower: $(BPFOBJ) | $(DEFAULT_BPFTOOL) $(RUNQSLOWER_OUTPUT)
 		    OUTPUT=$(RUNQSLOWER_OUTPUT) VMLINUX_BTF=$(VMLINUX_BTF)     \
 		    BPFTOOL_OUTPUT=$(HOST_BUILD_DIR)/bpftool/		       \
 		    BPFOBJ_OUTPUT=$(BUILD_DIR)/libbpf			       \
-		    BPFOBJ=$(BPFOBJ) BPF_INCLUDE=$(INCLUDE_DIR) &&	       \
+		    BPFOBJ=$(BPFOBJ) BPF_INCLUDE=$(INCLUDE_DIR)		       \
+		    EXTRA_CFLAGS='-g -O0 $(SAN_CFLAGS)'			       \
+		    EXTRA_LDFLAGS='$(SAN_LDFLAGS)' &&			       \
 		    cp $(RUNQSLOWER_OUTPUT)runqslower $@
 
 TEST_GEN_PROGS_EXTENDED += $(DEFAULT_BPFTOOL)
@@ -272,7 +274,8 @@ $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	   $(APIDIR)/linux/bpf.h					       \
 	   | $(BUILD_DIR)/libbpf
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
-		    EXTRA_CFLAGS='-g -O0'				       \
+		    EXTRA_CFLAGS='-g -O0 $(SAN_CFLAGS)'			       \
+		    EXTRA_LDFLAGS='$(SAN_LDFLAGS)'			       \
 		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
 
 ifneq ($(BPFOBJ),$(HOST_BPFOBJ))