selftests/bpf: Don't force lld on non-x86 architectures

LLVM's lld linker doesn't have a universal architecture support (e.g.,
it definitely doesn't work on s390x), so be safe and force lld for
urandom_read and liburandom_read.so only on x86 architectures.

This should fix s390x CI runs.

Fixes: 3e6fe5ce ("libbpf: Fix internal USDT address translation logic for shared libraries")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220617045512.1339795-1-andrii@kernel.org

tools/testing/selftests/bpf/Makefile

@@ -168,18 +168,25 @@ $(OUTPUT)/%:%.c
 	$(call msg,BINARY,,$@)
 	$(Q)$(LINK.c) $^ $(LDLIBS) -o $@
 
+# LLVM's ld.lld doesn't support all the architectures, so use it only on x86
+ifeq ($(SRCARCH),x86)
+LLD := lld
+else
+LLD := ld
+endif
+
 # Filter out -static for liburandom_read.so and its dependent targets so that static builds
 # do not fail. Static builds leave urandom_read relying on system-wide shared libraries.
 $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c
 	$(call msg,LIB,,$@)
 	$(Q)$(CLANG) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $^ $(LDLIBS)   \
-		     -fuse-ld=lld -Wl,-znoseparate-code -fPIC -shared -o $@
+		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -fPIC -shared -o $@
 
 $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
 	$(call msg,BINARY,,$@)
 	$(Q)$(CLANG) $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
 		     liburandom_read.so $(LDLIBS)			       \
-		     -fuse-ld=lld -Wl,-znoseparate-code	       		       \
+		     -fuse-ld=$(LLD) -Wl,-znoseparate-code		       \
 		     -Wl,-rpath=. -Wl,--build-id=sha1 -o $@
 
 $(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_testmod/*.[ch])